記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of Cosmology and Astroparticle Physics  

We investigate the formation of primordial black hole (PBH) based on numerical relativity simulations and peak theory as well as the corresponding scalar induced gravitational wave (SIGW) signals in the presence of logarithmic non-Gaussianities which has recently been confirmed in a wide class of inflation models. Through numerical calculations, we find certain parameter spaces of the critical thresholds for the type A PBH formation and reveal a maximum critical threshold value. We also find that there is a region where no PBH is produced from type II fluctuations contrary to a previous study. We then confirm that SIGW signals originated from the logarithmic non-Gaussianity are detectable in the Laser Interferometer Space Antenna if PBH account for whole dark matter. Finally, we discuss the SIGW interpretation of the nHz stochastic gravitational wave background reported by the recent pulsar timing array observations. We find that PBH overproduction is a serious problem for most of the parameter space, while this tension might still be alleviated in the non-perturbative regime.

DOI： 10.1088/1475-7516/2025/03/021

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Scopus

その他リンク： https://iopscience.iop.org/article/10.1088/1475-7516/2025/03/021/pdf

出版者・発行元：Physical Review D  

Gravitational waves (GWs) from gravitational three-body decay (graviton bremsstrahlung process) can leave an indelible signal at ultrahigh frequencies. We focus on a scenario where superheavy particles are produced gravitationally at a transition between the inflationary and kination phases and analyze the detectability of the signal in the presence of GWs generated from the vacuum fluctuations during inflation. We find that, in many cases, GWs from the graviton bremsstrahlung are buried in the stochastic gravitational wave background originating from inflation. However, if the superheavy particles are as heavy as the Planck scale, the graviton bremsstrahlung can produce a sizable amount of GWs, surpassing the inflationary ones.

DOI： 10.1103/PhysRevD.111.043511

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掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of Cosmology and Astroparticle Physics  

The curvature perturbation in a model of constant-roll (CR) inflation is interpreted in view of the logarithmic duality discovered in ref. [1] according to the δN formalism. We confirm that the critical value β:=φ̈/(Hφ̇)= -3/2 determining whether the CR condition is stable or not is understood as the point at which the dual solutions, i.e., the attractor and non-attractor solutions of the field equation, are interchanged. For the attractor-solution domination, the curvature perturbation in the CR model is given by a simple logarithmic mapping of a Gaussian random field, which can realise both the exponential tail (i.e., the single exponential decay) and the Gumbel-distribution-like tail (i.e., the double exponential decay) of the probability density function, depending on the value of β. Such a tail behaviour is important for, e.g., the estimation of the primordial black hole (PBH) abundance.

DOI： 10.1088/1475-7516/2025/02/042

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その他リンク： https://iopscience.iop.org/article/10.1088/1475-7516/2025/02/042/pdf

出版者・発行元：Physical Review D  

The subsolar mass primordial black hole (PBH) attracts attention as robust evidence of its primordial origin against the astrophysical black hole. Not only with themselves, PBHs can also form binaries with ordinary astrophysical objects, catching them by gravitational wave (GW) bremsstrahlung. We discuss the detectability of the inspiral GWs from binaries consisting of a PBH and a white dwarf (WD) by using space-borne gravitational wave interferometers like DECIGO. The conservative assessment shows the expected event number in three years by DECIGO is O(10-6) for MPBH∼0.1M⊙. Possible enhancement mechanisms of WD-PBH binary formation may amplify this event rate. We discuss how large enhancement associated with WDs is required to detect WD-PBH merger events without violating the existing constraints on the PBH-PBH merger by the ground-based detector.

DOI： 10.1103/PhysRevD.109.103514

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出版者・発行元：Journal of Cosmology and Astroparticle Physics  

The scalar-induced gravitational wave (SIGWs), arising from large amplitude primordial density fluctuations, provide a unique observational test for directly probing the epoch of inflation. In this work, we provide constraints on the SIGW background by taking into account the non-Gaussianity in the primordial density fluctuations, using the first three observing runs (O1-O3) data of the LIGO-Virgo-KAGRA collaboration. We find that the non-Gaussianity gives a non-negligible effect on the GW energy density spectrum and starts to affect the analysis of the O1-O3 data when the non-Gaussianity parameter is F <inf>NL</inf> > 3.55. Furthermore, the constraints exhibit asymptotic behavior given by F <inf>NL</inf> A<inf>g</inf> = const. at large F <inf>NL</inf> limit, where A<inf>g</inf> denotes the amplitude of the curvature perturbations. In the limit of large F <inf>NL</inf>, we placed a 95% credible level upper limit F <inf>NL</inf> A<inf>g</inf> ≤ 0.115, 0.106, 0.112 at fixed scales of 10¹⁶, 10^16.5, 10¹⁷ Mpc^-1, respectively.

DOI： 10.1088/1475-7516/2024/05/082

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出版者・発行元：General Relativity and Gravitation  

Abstract: A modification to the vis-viva equation that accounts for general relativistic effects is introduced to enhance the accuracy of predictions of orbital motion and precession. The updated equation reduces to the traditional vis-viva equation under Newtonian conditions and is a more accurate tool for astrodynamics than the traditional equation. Preliminary simulation results demonstrate the application potential of the modified vis-viva equation for more complex n-body systems. Spherical symmetry is assumed in this approach; however, this limitation could be removed in future research. This study is a pivotal step toward bridging classical and relativistic mechanics and thus makes an important contribution to the field of celestial dynamics. Graphical abstract: (Figure presented.).

DOI： 10.1007/s10714-024-03235-7

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出版者・発行元：Astrophysical Journal  

Numerous observations have shown that almost all galaxies in our Universe host supermassive black holes (SMBHs), but there is still much debate about their formation and evolutionary processes. Recently, gravitational waves (GWs) have been expected to be a new and important informative observation, in particular, in the low-frequency region by making use of the Laser Interferometer Space Antenna (LISA) and Pulsar Timing Arrays (PTAs). As an evolutionary process of the SMBHs, we revisit a dark matter (DM) halo-SMBH coevolution model based on the halo merger tree employing an ansatz for the mass relation between the DM halos and the SMBHs at z = 6. In this model, the mass of SMBHs grows through their mergers associated with the halo mergers, and hence, the evolutionary information must be stored in the GWs emitted at the mergers. We investigate the stochastic gravitational background from the coalescing SMBH binaries, which the PTAs can detect, and also the GW bursts emitted at the mergers, which can be detected by the mHz band observations such as LISA. We also discuss the possibility of probing the mass relation between the DM halos and the SMBHs at high redshift by future GW observations.

DOI： 10.3847/1538-4357/ad088f

Open Access

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1103/PhysRevD.106.103529

担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1088/1475-7516/2022/11/021

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Physical Review D  

The juggled interferometer (JIFO) is an Earth-based gravitational wave detector using repeatedly free-falling test masses. With no worries of seismic noise and suspension thermal noise, the JIFO can have much better sensitivity at lower frequencies than the current Earth-based gravitational wave detectors. The data readout method of a JIFO could be challenging if one adopts the fringe-locking method. We present a phase reconstruction method in this paper by building up a complex function which has a fringe-independent signal-To-noise ratio. Considering the displacement noise budget of the Einstein Telescope (ET), we show that the juggled test masses significantly improve the sensitivity at 0.1-2.5 Hz even with discontinuous data. The science cases brought with the improved sensitivity would include detecting quasinormal modes of black holes with 104-105 M, testing Brans-Dicke theory with black-hole and neutron-star inspirals, and detecting primordial-black-hole-related gravitational waves.

DOI： 10.1103/PhysRevD.106.042007

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of Cosmology and Astroparticle Physics  

In this work, we have performed numerical simulations of primordial black hole (PBH) formation in the Friedman-Lemaître-Robertson-Walker universe filled by radiation fluid, introducing the local-type non-Gaussianity to the primordial curvature fluctuation. We have compared the numerical results from simulations with previous analytical estimations on the threshold value for PBH formation done in the previous paper [1], particularly for negative values of the non-linearity parameter f NL. Our numerical results show the existence of PBH formation of (the so-called) type I also in the case f NL ≤2-0.336, which was not found in the previous analytical expectations using the critical averaged compaction function. In particular, although the universal value for the averaged critical compaction function ō o = 2/5 found previously in the literature is not satisfied for all the profiles considered in this work, an alternative direct analytical estimate has been found to be roughly accurate to estimate the thresholds, which gives the value of the critical averaged density with a few % deviation from the numerical one for f NL ≤3-1.

DOI： 10.1088/1475-7516/2022/05/012

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Galaxies  

The DECi-hertz Interferometer Gravitational-Wave Observatory (DECIGO) is a space gravitational wave (GW) detector. DECIGO was originally designed to be sensitive enough to observe primordial GW background (PGW). However, due to the lowered upper limit of the PGW by the Planck observation, further improvement of the target sensitivity of DECIGO is required. In the previous studies, DECIGO’s parameters were optimized to maximize the signal-to-noise ratio (SNR) of the PGW to quantum noise including the effect of diffraction loss. To simulate the SNR more realistically, we optimize DECIGO’s parameters considering the GWs from double white dwarfs (DWDs) and the thermal noise of test masses. We consider two cases of the cutoff frequency of GWs from DWDs. In addition, we consider two kinds of thermal noise: thermal noise in a residual gas and internal thermal noise. To investigate how the mirror geometry affects the sensitivity, we calculate it by changing the mirror mass, keeping the mirror thickness, and vice versa. As a result, we obtained the optimums for the parameters that maximize the SNR that depends on the mirror radius. This result shows that a thick mirror with a large radius gives a good SNR and enables us to optimize the design of DECIGO based on the feasibility study of the mirror size in the future.

DOI： 10.3390/galaxies10010025

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記述言語：日本語   出版者・発行元：一般社団法人 日本物理学会  

DOI： 10.11316/jpsgaiyo.77.2.0_443

Open Access

CiNii Research

出版者・発行元：Progress of Theoretical and Experimental Physics  

The Deci-hertz Interferometer Gravitational Wave Observatory (DECIGO) is a future Japanese space mission with a frequency band of 0.1 Hz to 10 Hz. DECIGO aims at the detection of primordial gravitational waves, which could have been produced during the inflationary period right after the birth of the Universe. There are many other scientific objectives of DECIGO, including the direct measurement of the acceleration of the expansion of the Universe, and reliable and accurate predictions of the timing and locations of neutron star/black hole binary coalescences. DECIGO consists of four clusters of observatories placed in heliocentric orbit. Each cluster consists of three spacecraft, which form three Fabry-Pérot Michelson interferometers with an arm length of 1000 km. Three DECIGO clusters will be placed far from each other, and the fourth will be placed in the same position as one of the other three to obtain correlation signals for the detection of primordial gravitational waves. We plan to launch B-DECIGO, which is a scientific pathfinder for DECIGO, before DECIGO in the 2030s to demonstrate the technologies required for DECIGO, as well as to obtain fruitful scientific results to further expand multi-messenger astronomy.

DOI： 10.1093/ptep/ptab019

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Progress of Theoretical and Experimental Physics  

Computations of the primordial black hole (PBH) mass function discussed in the literature have conceptual issues. They stem from the fact that the mass function is a differential quantity and the standard criterion of the PBH formation from the seed primordial fluctuations cannot be directly applied to the computation of the differential quantities. We propose a new criterion of the PBH formation, which is the addition of one extra condition to the existing one. By doing this, we derive a formal expression of the PBH mass function without introducing any ambiguous interpretations that exist in the previous studies. Once the underlying primordial fluctuations are specified, the PBH mass function can be in principle determined by the new formula. As a demonstration of our formulation, we compute the PBH mass function analytically for the case where the perturbations are Gaussian and the space is 1 dimension.

DOI： 10.1093/ptep/ptaa011

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出版者・発行元：Asian Smallholders in Comparative Perspective  

This chapter reviews pertinent issues facing Japanese smallholders and explores the role of small-scale farming households in contemporary japan. Here, the influences of agricultural policy and technological innovations on smallholders are considered alongside reviews of key regional differences in Japanese agriculture, based on geographical terrain, management scale and labour force organization. Research reveals that the small-scale nature of household farms, ageing, and a lack of successors are some of the major factors - among others - threatening the persistence of smallholder agriculture in Japan.

DOI： 10.5117/9789462988170/CH03

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出版者・発行元：Open Medical Imaging Journal  

In order to clarify the relationship among grammatical knowledge, processing components, and neural substrates in sentence comprehension, we used functional magnetic resonance imaging to investigate how brain activation is affected by two types of scrambling (short scrambling and middle scrambling) in ditransitive sentences in Japanese. Short scrambling and middle scrambling enhanced activation in the anterior and posterior left inferior frontal gyrus respectively. This finding accords with the view that the anterior left inferior frontal gyrus is involved in the automatic processing that establishes a dependency relation between a verb and its arguments, and the posterior left inferior frontal gyrus supports this kind of processing through its role in verbal working memory. This result is more congruent with a process-based approach to neural bases for sentence processing, which searches for neurological correlates of psycholinguistically defined processing components, than with a grammar-based approach, which probes neural networks with the assumption that major grammatical operations are neurologically individuated. © Koizumi et al.

DOI： 10.2174/1874347101206010070

Scopus

出版者・発行元：Progress of Theoretical Physics Supplement  

We discuss generation of non-Gaussianity in primordial density perturbation through the super-horizon evolution during inflation by using the so-called δN formalism. In order to discuss the difficulties of generating large local-type non-Gaussianity during inflation, we discuss Kadota-Stewart model. This model gives an example in which we have to choose rather unnatural initial conditions even if large non-Gaussianity can be generated.

DOI： 10.1143/PTP.190.135

Scopus

出版者・発行元：Proceedings of the 21st Workshop on General Relativity and Gravitation in Japan Jgrg 2011  

We investigate a statistical anisotropy on the Cosmic Microwave Background (CMB) bispectrum, which can be generated from the primordial non-Gaussianity induced by quantum uctuations of a vector field. We find new congurations in the multipole space of the CMB bispectrum given by ℓ<inf>1</inf> = ℓ<inf>2</inf>+ℓ<inf>3</inf>+2/ℓ<inf>2</inf> - ℓ<inf>3</inf> - 2 and their permuta- Tions, which violate the rotational invariance, such as an off-diagonal conguration in the CMB power spectrum. We also find that in a model presented by Yokoyama and Soda (2008), the amplitude of the statistically anisotropic bispectrum in the above configurations becomes as large as that in other configurations such as ℓ<inf>1</inf> = ℓ<inf>2</inf> + ℓ<inf>3</inf>. As a result, it might be possible to detect these contributions in future experiments, which would give us novel information about the physics of the early Universe.

Scopus

出版者・発行元：Proceedings of the 19th Workshop on General Relativity and Gravitation in Japan Jgrg 2009  

We present a mechanism of generating the primordial curvature perturbation at the end of thermal inflation utilizing a fluctuating coupling of a flaton field with the fields in thermal bath. We also discuss non-Gaussianity in the mechanism and show that large non-Gaussianity can be generated in this scenario.

Scopus

出版者・発行元：Proceedings of the 18th Workshop on General Relativity and Gravitation in Japan Jgrg 2008  

We study an anisotropic inflationary scenario. We show that the universe undergoes anisotropic inflationary expansion due to a preferred direction determined by a vector. In particular, it is stressed that primordial gravitational waves can be induced from curvature perturbations. Hence, even in low scale inflation, a sizable amount of primordial gravitational waves may be produced during inflation. To verify this expectation, we study perturbations in the anisotropic inflationary background.

DOI： 10.1088/1475-7516/2008/08/034

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of Cosmology and Astroparticle Physics  

Primordial black holes (PBHs) whose masses are in ∼ [10^-15 M <inf>⊙</inf>,10^-11 M <inf>⊙</inf>] have been extensively studied as a candidate of whole dark matter (DM). One of the probes to test such a PBH-DM scenario is scalar-induced stochastic gravitational waves (GWs) accompanied with the enhanced primordial fluctuations to form the PBH with frequency peaked in the mHz band being targeted by the LISA mission. In order to utilize the stochastic GW for checking the PBH-DM scenario, it needs to exactly relate the PBH abundance and the amplitude of the GW spectrum. Recently in Kitajima et al. [1], the impact of the non-Gaussianity of the enhanced primordial curvature perturbations on the PBH abundance has been investigated based on the peak theory, and they found that a specific non-Gaussian feature called the exponential tail significantly increases the PBH abundance compared with the Gaussian case. In this work, we investigate the spectrum of the induced stochastic GW associated with PBH DM in the exponential-tail case. In order to take into account the non-Gaussianity properly, we employ the diagrammatic approach for the calculation of the spectrum. We find that the amplitude of the stochastic GW spectrum is slightly lower than the one for the Gaussian case, but it can still be detectable with the LISA sensitivity. We also find that the non-Gaussian contribution can appear on the high-frequency side through their complicated momentum configurations. Although this feature emerges under the LISA sensitivity, it might be possible to obtain information about the non-Gaussianity from GW observation with a deeper sensitivity such as the DECIGO mission.

DOI： 10.1088/1475-7516/2023/05/044

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その他リンク： https://iopscience.iop.org/article/10.1088/1475-7516/2023/05/044/pdf

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Progress of Theoretical and Experimental Physics  

Since the discovery of the accelerated expansion of the present universe, significant theoretical developments have been made in the area of modified gravity. In the meantime, cosmological observations have been providing more high-quality data, allowing us to explore gravity on cosmological scales. To bridge the recent theoretical developments and observations, we present an overview of a variety of modified theories of gravity and the cosmological observables in the cosmic microwave background and large-scale structure, supplemented with a summary of predictions for cosmological observables derived from cosmological perturbations and sophisticated numerical studies. We specifically consider scalar-tensor theories in the Horndeski and DHOST family, massive gravity/bigravity, vector-tensor theories, metric-affine gravity, and cuscuton/minimally modified gravity, and discuss the current status of those theories with emphasis on their physical motivations, validity, appealing features, the level of maturity, and calculability. We conclude that the Horndeski theory is one of the most well-developed theories of modified gravity, although several remaining issues are left for future observations. The paper aims to help to develop strategies for testing gravity with ongoing and forthcoming cosmological observations.

DOI： 10.1093/ptep/ptad052

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掲載種別：研究論文（学術雑誌）   出版者・発行元：Physical Review D  

Recently, the cross-correlation between E- and B-mode polarization of the cosmic microwave background, which is well explained by cosmic birefringence with rotation angle β≈0.3 deg, has been found in cosmic microwave background polarization data. We carefully investigate the possibility of explaining the observed EB correlation by the primordial chiral gravitational waves, which can be generated in the parity-violating theories in the primordial Universe. We found that the chiral gravitational wave scenario does not work due to the overproduction of the BB autocorrelation, which far exceeds the observed one by SPTPol and POLARBEAR.

DOI： 10.1103/PhysRevD.106.103529

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Astrophysical Journal  

We investigate the probability distribution of the effective inspiral spin, the mass ratio, and the chirp mass of primordial black hole (PBH) binaries, incorporating the effect of the critical phenomena of gravitational collapse. As a leading order estimation, each binary is assumed to be formed from two PBHs that are randomly chosen according to the probability distribution of single PBHs, and the accretion effects on the mass and spin of each PBH are not considered for simplicity. We find that, although the critical phenomena can lead to large spins on the low-mass tail, the effective inspiral spin of the binary is statistically very small, 〈 χ e f f 2 〉 ∼ 10 − 3 . We also see that there is almost no anticorrelation between the effective inspiral spin and the mass ratio, which can be inferred from observations.

DOI： 10.3847/1538-4357/ac93f1

Open Access

Web of Science

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of Cosmology and Astroparticle Physics  

Motivated by the result of Planck+BICEP/Keck recently released, we investigate the consistency of the multi-field inflation models in terms of the spectral index n<inf>s</inf> and the tensor-to-scalar ratio r. In this study, we focus on double-inflaton models with and without a spectator field. We find that inflaton with a quadratic potential can become viable when three fields with a specific hierarchical mass spectrum are realized such that two fields act as inflatons and the other one is the spectator. We also discuss the conditions to avoid the fine-tuning, by careful study of how the prediction depends on the background trajectory in the inflaton-field space.

DOI： 10.1088/1475-7516/2022/07/042

DOI： 10.1088/1475-7516/2022/07/042

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その他リンク： https://iopscience.iop.org/article/10.1088/1475-7516/2022/07/042/pdf

掲載種別：研究論文（学術雑誌）   出版者・発行元：Publications of the Astronomical Society of Japan  

In the most distant reaches of the Universe, the 21 cm hyperfine transition in neutral hydrogen provides one of the only available tracers of large-scale structure. A number of instruments have been working or are planned to measure the 21 cm line signals, and in particular, the Experiment to Detect the Global EoR Signature (EDGES) has recently reported the first detection of an absorption signal, which corresponds to the 21 cm line global signal at the epoch of reionization (EoR). The future large radio telescope, the Square Kilometre Array (SKA) will be able to deliver the high-precision measurement of the 21 cmline emission/absorption signals. In this paper, we review the current status for the 21 cmline global and fluctuation signals from EoR to the dark ages, and then summarize the recent studies of how we probe the primordial Universe particularly motivated by the recent EDGES result and future observations by SKA. We focus on two applications for constraining cosmology with the EDGES result: constraints on the primordial magnetic fields and those on the primordial power spectrum.We also discuss the potential of future SKA for probing the inflationary Universe, by discussing expected constraints on the primordial power spectrum, its adiabaticity, and primordial non-Gaussianities from future observations of 21cm fluctuations.

DOI： 10.1093/pasj/psac015

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Publications of the Astronomical Society of Japan  

We revisit a possible scale-dependence of local-type primordial non-Gaussianities induced by super-horizon evolution of scalar field perturbations. We develop the formulation based on δN formalism and derive the generalized form of the local-type bispectrum and also trispectrum which allows us to implement the scale-dependence and suitably compare model prediction with observational data. We propose simple but phenomenologically meaningful expressions, which encompass the information of a wide range of physically motivated models. We also formulate a large-scale power spectrum and bispectrum of biased objects in the presence of the scale-dependent primordial non-Gaussianities. We perform the Fisher analysis for future galaxy surveys and give the projected constraints on the parameters of the generalized local-form of primordial non-Gaussianities.

DOI： 10.1093/pasj/psab108

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of Cosmology and Astroparticle Physics  

In this paper, we update the peak theory for the estimation of the primordial black hole (PBH) abundance, particularly by implementing the critical behavior in the estimation of the PBH mass and employing the averaged compaction function for the PBH formation criterion to relax the profile dependence. We apply our peak theory to a specific non-Gaussian feature called the exponential tail, which is characteristic in ultra slow-roll models of inflation. With this type of non-Gaussianity, the probability of a large perturbation is not suppressed by the Gaussian factor but decays only exponentially, so the PBH abundance is expected to be much enhanced. Not only do we confirm this enhancement even compared to the case of the corresponding nonlinearity parameter f NL = 5/2, but also we find that the resultant PBH mass spectrum has a characteristic maximal mass which is not seen in the simple Press-Schechter approach.

DOI： 10.1088/1475-7516/2021/10/053

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その他リンク： https://iopscience.iop.org/article/10.1088/1475-7516/2021/10/053/pdf

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Physical Review D  

We motivate a minimal realization of slow-roll k-inflation by incorporating the local conformal symmetry and the broken global SO(1,1) symmetry in the metric-affine geometry. With use of the metric-affine geometry where both the metric and the affine connection are treated as independent variables, the local conformal symmetry can be preserved in each term of the Lagrangian and thus higher derivatives of scalar fields can be easily added in a conformally invariant way. Predictions of this minimal slow-roll k-inflation, ns∼0.96, r∼0.005, and cs∼0.03, are not only consistent with current observational data but also have a prospect to be tested by forthcoming observations.

DOI： 10.1103/physrevd.103.l101303

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その他リンク： http://harvest.aps.org/v2/journals/articles/10.1103/PhysRevD.103.L101303/fulltext

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of Cosmology and Astroparticle Physics  

We develop a possibility of generating tensor non-Gaussianity in a kind of anisotropic inflation, where a U(1) gauge field is kinetically coupled to a spectator scalar field. Owing to this coupling, the coherent mode of the electric field appears and softly breaks the isotropy of the Universe. We compute the bispectrum of linearly-polarized tensor perturbations sourced by the gauge field and find that it is strongly red-tilted and has distinctive statistical anisotropies including higher-order multipole moments. Interestingly, the tensor bispectra with the specific combinations of linear polarization modes are dominant, and their amplitudes depend on the different sets of multipole moments. This new type of statistically-anisotropic tensor non-Gaussianity can be potentially testable with the upcoming cosmic microwave background B-mode polarization experiments.

DOI： 10.1088/1475-7516/2021/03/047

Open Access

Web of Science

Scopus

その他リンク： https://iopscience.iop.org/article/10.1088/1475-7516/2021/03/047/pdf

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of Cosmology and Astroparticle Physics  

We discuss the possibility of explaining the recent NANOGrav results by inationary gravitational waves (IGWs) with a blue-tilted primordial spectrum. Although such IGWs can account for the NANOGrav signal without contradicting the upper bound on the tensor-to-scalar ratio at the cosmic microwave background scale, the predicted spectrum is in strong tension with the upper bound on the amplitude of the stochastic gravitational wave background by big-bang nucleosynthesis (BBN) and the second LIGO-Virgo observation run. However, the thermal history of the Universe, such as reheating and late-time entropy production, affects the spectral shape of IGWs at high frequencies and permits evading the upper bounds. We show that, for the standard reheating scenario, when the reheating temperature is relatively low, a blue tensor spectrum can explain the recent NANOGrav signal without contradicting the BBN and the LIGO-Virgo constraints. We further find that, when one considers a late-time entropy production, the NANOGrav signal can be explained even for an instant reheating scenario. c 2021 IOP Publishing Ltd and Sissa Medialab.

DOI： 10.1088/1475-7516/2021/01/071

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その他リンク： https://iopscience.iop.org/article/10.1088/1475-7516/2021/01/071

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Physical Review D  

We study matter density perturbations up to third order and the one-loop matter power spectrum in degenerate higher-order scalar-tensor (DHOST) theories beyond Horndeski. We systematically solve gravitational field equations and fluid equations order by order and find three novel shape functions characterizing the third-order solution in DHOST theories. A complete form of the one-loop matter power spectrum is then obtained using the resultant second- and third-order solutions. We confirm the previous result that the convergence condition of the loop integrals in the infrared limit becomes more stringent than that of the standard one in general relativity. We show that also in the ultraviolet limit the convergence condition becomes more stringent and the one-loop matter power spectrum is thus sensitive to the short-wavelength behavior of the linear power spectrum.

DOI： 10.1103/physrevd.102.103505

Web of Science

Scopus

その他リンク： http://harvest.aps.org/v2/journals/articles/10.1103/PhysRevD.102.103505/fulltext

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Epl  

Systematic understanding for classes of inflationary models is investigated from the viewpoint of the local conformal symmetry and the slightly broken global symmetry in the framework of the metric-affine geometry. In the metric-affine geometry, which is a generalisation of the Riemannian one adopted in the ordinary General Relativity, the affine connection is an independent variable of the metric rather than being given, e.g., by the Levi-Civita connection as its function. Thanks to this independency, the metric-affine geometry can preserve the local conformal symmetry in each term of the Lagrangian contrary to the Riemannian geometry, and then the local conformal invariance can be compatible with much more kinds of global symmetries. As simple examples, we consider the two-scalar models with the broken SO(1,1) or O(2), leading to the well-known α-attractor or natural inflation, respectively. The inflaton, can be understood as their pseudo-Nambu-Goldstone boson.

DOI： 10.1209/0295-5075/132/39001

Web of Science

Scopus

その他リンク： https://iopscience.iop.org/article/10.1209/0295-5075/132/39001/pdf

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Physical Review D  

We show that a nonminimal coupling to gravity can not only make some inflationary models consistent with cosmological data, similar to the case of Higgs inflation, but can also invoke slow-roll violation to realize a graceful exit from inflation. In particular, this is the case in models where a destabilizing mechanism that ends inflation should be assumed when the model is minimally coupled to gravity. As explicit examples, we consider the power-law and inverse monomial inflation models with a nonminimal coupling to gravity. While these models are excluded in the minimally coupled case, we show that they can become viable again in nonminimally coupled scenarios. In most scenario we considered, reheating can be naturally realized via gravitational particle production but this depends on the underlying theory of gravity in a nontrivial way reheating can be naturally realized via gravitational particle production but that this depends on the underlying theory of gravity in a nontrivial way.

DOI： 10.1103/physrevd.102.043524

Web of Science

Scopus

その他リンク： http://harvest.aps.org/v2/journals/articles/10.1103/PhysRevD.102.043524/fulltext

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of Cosmology and Astroparticle Physics  

Primordial magnetic field (PMF) is one of the feasible candidates to explain observed large-scale magnetic fields, for example, intergalactic magnetic fields. We present a new mechanism that brings us information about PMFs on small scales based on the abundance of primordial black holes (PBHs). The anisotropic stress of the PMFs can act as a source of the super-horizon curvature perturbation in the early universe. If the amplitude of PMFs is sufficiently large, the resultant density perturbation also has a large amplitude, and thereby, the PBH abundance is enhanced. Since the anisotropic stress of the PMFs is consist of the square of the magnetic fields, the statistics of the density perturbation follows the non-Gaussian distribution. {Assuming Gaussian distributions and delta-function type power spectrum for PMFs, based on a Monte-Carlo method, we obtain an approximate probability density function of the density perturbation, and it is an important piece to relate the amplitude of PMFs with the abundance of PBHs.} Finally, we place the strongest constraint on the amplitude of PMFs as a few hundred nano-Gauss on 10² Mpc^-1 k 10¹⁸ Mpc^-1 where the typical cosmological observations never reach.

DOI： 10.1088/1475-7516/2020/05/039

Web of Science

Scopus

arXiv

その他リンク： https://iopscience.iop.org/article/10.1088/1475-7516/2020/05/039

Computations of the primordial black hole (PBH) mass function discussed in
the literature have conceptual issues. They stem from that the mass function is
a differential quantity and the standard criterion of the PBH formation from
the seed primordial fluctuations cannot be directly applied to the computation
of the differential quantities. We propose a new criterion of the PBH formation
which is an addition of one extra condition to the existing one. By doing this,
we derive a formal expression of the PBH mass function without introducing any
ambiguous interpretations which exist in the previous studies. Once the
underlying primordial fluctuations are specified, the PBH mass function can be
in principle determined by the new formula. As a demonstration of our
formulation, we compute the PBH mass function analytically for the case where
the perturbations are Gaussian and the space is one dimension.

arXiv

出版者・発行元：Physical Review D  

In the presence of the local-type primordial non-Gaussianity, it is known that the clustering of primordial black holes (PBHs) emerges even on superhorizon scales at the formation time. This effect has been investigated in the high-peak limit of the PBH formation in the radiation-dominated epoch in the literature. There is another possibility that the PBH formation takes place in the early matter-dominated epoch. In this scenario, the high-peak limit is not applicable because even initially small perturbations grow and can become a PBH. We first derive a general formula to estimate the clustering of PBHs with primordial non-Gaussianity without assuming the high-peak limit and then apply this formula to a model of PBH formation in a matter-dominated epoch. Clustering is less significant in the case of the PBH formation in the matter-dominated epoch than that in the radiation-dominated epoch. Nevertheless, it is much larger than the Poisson shot noise in many cases. Relations to the constraints of the isocurvature perturbations by the cosmic microwave background radiation are quantitatively discussed.

DOI： 10.1103/PhysRevD.100.123544

Web of Science

Scopus

arXiv

出版者・発行元：Journal of Cosmology and Astroparticle Physics  

In this paper, we fully investigate cosmological scenarios in which dark matter is non-minimally coupled to an extra scalar degree of freedom. The interaction is realized by means of conformal and disformal terms in the transformed gravitational metric. Considering linear perturbation theory, we show that the growth rate of dark matter differs from the uncoupled case and that the well-known Kaiser formula undergoes modification. As a result, redshift space distortion measurements cease to be a direct probe of the linear growth rate of total matter, since the distortion factor has an extra, coupling-dependent term. We study the effect of the coupling in three cosmological models, two conformally and one disformally coupled, and forecast the constraints on the coupling, and other cosmological parameters, from future galaxy surveys.

DOI： 10.1088/1475-7516/2019/10/049

Web of Science

Scopus

arXiv

DOI： 10.1103/PhysRevD.100.023537

Web of Science

arXiv

出版者・発行元：Journal of Cosmology and Astroparticle Physics  

We discuss the effect of local type non-Gaussianity on the abundance of primordial black holes (PBH) based on the peak theory. We provide the PBH formation criterion based on the so-called compaction function and use the peak theory statistics associated with the curvature perturbation with the local type non-Gaussianity. Providing a method to estimate the PBH abundance, we demonstrate the effects of non-Gaussianity. It is explicitly shown that the value of non-linear parameter |f<inf>NL</inf>| ∼ 1 induces a similar effect to a few factors of difference in the amplitude of the power spectrum.

DOI： 10.1088/1475-7516/2019/09/033

Web of Science

Scopus

arXiv

出版者・発行元：Progress of Theoretical and Experimental Physics  

We formulate the two-point correlation function of primordial black holes (PBHs) at their formation time, based on the functional integration approach which has often been used in the context of halo clustering. We find that PBH clustering on super-Hubble scales could never be induced in the case where the initial primordial fluctuations are Gaussian, while it can be enhanced by the so-called local-type trispectrum (four-point correlation function) of the primordial curvature perturbations.

DOI： 10.1093/ptep/ptz105

Open Access

Web of Science

Scopus

arXiv

その他リンク： http://arxiv.org/pdf/1906.04958v2

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1103/PhysRevD.99.104051

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Monthly Notices of the Royal Astronomical Society  

Spatially fluctuating primordial magnetic fields (PMFs) inhomogeneously reheat the Universe when they dissipate deep inside the horizon before recombination. Such an energy injection turns into an additional photon temperature perturbation. We investigate secondary cosmic microwave background (CMB) temperature anisotropies originated from this mechanism, which we call inhomogeneous magnetic reheating. We find that it can bring us information about non-linear coupling between PMFs and primordial curvature perturbations parametrized by b<inf>NL</inf>, which should be important for probing the generation mechanism of PMFs. In fact, by using current CMB observations, we obtain an upper bound on the non-linear parameter as log (b<inf>NL</inf>(B<inf>λ</inf>/nG)²) ≲− 36.5n<inf>B</inf> − 94.0 with B<inf>λ</inf> and n<inf>B</inf> being a magnetic field amplitude smoothed over λ = 1 Mpc scale and a spectral index of the PMF power spectrum, respectively. Our constraints are far stronger than a previous forecast based on the future CMB spectral distortion anisotropy measurements because inhomogeneous magnetic reheating covers a much wider range of scales, i.e. 1 Mpc⁻¹ ≲ k ≲ 10¹⁵ Mpc⁻¹

DOI： 10.1093/mnras/stz2882

Web of Science

Scopus

arXiv

掲載種別：研究論文（学術雑誌）   出版者・発行元：Physical Review D  

We constrain the abundance of primordial black holes (PBH) using 2622 microlensing events obtained from 5-years observations of stars in the Galactic bulge by the Optical Gravitational Lensing Experiment (OGLE). The majority of microlensing events display a single or at least continuous population that has a peak around the light curve timescale tE≃20 days and a wide distribution over the range tE≃[1,300] days, while the data also indicates a second population of 6 ultrashort-timescale events in tE≃[0.1,0.3] days, which are advocated to be due to free-floating planets. We confirm that the main population of OGLE events can be well modeled by microlensing due to brown dwarfs, main sequence stars and stellar remnants (white dwarfs and neutron stars) in the standard Galactic bulge and disk models for their spatial and velocity distributions. Using the dark matter (DM) model for the Milky Way (MW) halo relative to the Galactic bulge/disk models, we obtain the tightest upper bound on the PBH abundance in the mass range MPBH≃[10-6,10-3] M (Earth-Jupiter mass range), if we employ the "null hypothesis" that the OGLE data does not contain any PBH microlensing event. More interestingly, we also show that Earth-mass PBHs can well reproduce the 6 ultrashort-timescale events, without the need of free-floating planets, if the mass fraction of PBH to DM is at a per cent level, which is consistent with other constraints such as the microlensing search for Andromeda galaxy (M31) and the longer timescale OGLE events. Our result gives a hint of PBH existence, and can be confirmed or falsified by microlensing search for stars in M31, because M31 is towards the MW halo direction and should therefore contain a much less number of free-floating planets, even if exist, than the direction to the MW center.

DOI： 10.1103/physrevd.99.083503

Web of Science

Scopus

arXiv

その他リンク： http://harvest.aps.org/v2/journals/articles/10.1103/PhysRevD.99.083503/fulltext

出版者・発行元：Physical Review D  

We investigate the potential of cosmological observations, such as galaxy surveys, for constraining degenerate higher-order scalar-tensor (DHOST) theories, focusing in particular on the linear growth of the matter density fluctuations. We develop a formalism to describe the evolution of the matter density fluctuations during the matter dominated era and in the early stage of the dark energy dominated era in DHOST theories, and give an approximate expression for the gravitational growth index in terms of several parameters characterizing the theory and the background solution under consideration. By employing the current observational constraints on the growth index, we obtain a new constraint on a parameter space of DHOST theories. Combining our result with other constraints obtained from the Newtonian stellar structure, we show that the degeneracy between the effective parameters of DHOST theories can be broken without using the Hulse-Taylor pulsar constraint.

DOI： 10.1103/PhysRevD.99.104051

Web of Science

Scopus

arXiv

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Physical Review D  

Primordial magnetic fields (PMFs) can source gravitational wave background (GWB). In this paper, we investigate the possible constraints on small-scale PMF considering the ongoing and forthcoming direct detection observations of GWB. In contrast to the conventional cosmological probes, e.g., cosmic microwave background anisotropies, which are useful to investigate large-scale PMFs (>1 Mpc), the direct detection experiments of GWB can explore small-scale PMFs whose scales correspond to the observed frequencies of GWB. We show that future ground-based or space-based interferometric gravitational wave detectors give a strong constraint of about 102 nG on much smaller scales of about k≈1012 Mpc-1. We also demonstrate that pulsar timing arrays have a potential to strongly constrain PMFs. The current limits on GWB from pulsar timing arrays can put the tight constraint on the amplitude of the PMFs of about 30 nG whose coherent length is about k≈106 Mpc-1. The future experiments for the direct detection of GWB by the Square Kilometre Array could give much tighter constraints on the amplitude of PMFs of about 5 nG on k≈106 Mpc-1, on which scales it is difficult to reach by using the cosmological observations.

DOI： 10.1103/physrevd.98.083518

Web of Science

Scopus

その他リンク： http://harvest.aps.org/v2/journals/articles/10.1103/PhysRevD.98.083518/fulltext

掲載種別：研究論文（学術雑誌）   出版者・発行元：Physical Review D  

We investigate the possibility of constraining statistical anisotropies of the primordial tensor perturbations by using future observations of the cosmic microwave background (CMB) B-mode polarization. By parametrizing a statistically anisotropic tensor power spectrum as Ph(k)=Ph(k)ngncosnθk, where θk is an angle of the direction of k^=k/k from a preferred direction, we find that it is possible for future B-mode observations such as CMB-S4 to detect the tensor statistical anisotropy at the level of gn∼O(0.1).

DOI： 10.1103/PhysRevD.98.083522

Web of Science

Scopus

arXiv

その他リンク： http://arxiv.org/pdf/1808.08044v1

DOI： 10.1103/PhysRevLett.121.059901

PubMed

掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of Cosmology and Astroparticle Physics  

We investigate future constraints on primordial local-type non-Gaussianity from 21 cm angular power spectrum from minihalos. We particularly focus on the trispectrum of primordial curvature perturbations which are characterized by the non-linearity parametersτ <inf>NL</inf> and g <inf>NL</inf> . We show that future measurements of minihalo 21 cm angular power spectrum can probe these non-linearity parameters with an unprecedented precision of τ <inf>NL</inf> ∼ 30 and g <inf>NL</inf> ∼ 2 × 10 ³ for Square Kilometre Array (SKA) and τ <inf>NL</inf> ∼ 0.6 and g <inf>NL</inf> ∼ 8 × 10 ² for Fast Fourier Transform Telescope (FFTT). These levels of sensitivity would give significant implications for models of the inflationary Universe and the origin of cosmic density fluctuations.

DOI： 10.1088/1475-7516/2019/02/033

Web of Science

Scopus

arXiv

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Physical Review D  

The Horndeski scalar-tensor theory and its recent extensions allow nonlinear derivative interactions of the scalar degree of freedom. We study the matter bispectrum of large scale structure as a probe of these modified gravity theories, focusing in particular on the effect of the terms that newly appear in the so-called "beyond Horndeski" theories. We derive the second-order solution for the matter density perturbations and find that the interactions beyond Horndeski lead to a new time-dependent coefficient in the second-order kernel which differs in general from the standard value of general relativity and the Horndeski theory. This can deform the matter bispectrum at the folded triangle configurations (k1+k2=k3), while it is never possible within the Horndeski theory.

DOI： 10.1103/PhysRevD.97.103517

Web of Science

Scopus

arXiv

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of Cosmology and Astroparticle Physics  

Measurements of 21 cm line fluctuations from minihalos have been discussed as a powerful probe of a wide range of cosmological models. However, previous studies have taken into account only the pixel variance, where contributions from different scales are integrated. In order to sort out information from different scales, we formulate the angular power spectrum of 21 cm line fluctuations from minihalos at different redshifts, which can enhance the constraining power enormously. By adopting this formalism, we investigate expected constraints on parameters characterizing the primordial power spectrum, particularly focusing on the spectral index n<inf>s</inf> and its runnings α<inf>s</inf> and β<inf>s</inf>. We show that future observations of 21 cm line fluctuations from minihalos, in combination with cosmic microwave background, can potentially probe these runnings as α<inf>s</inf> ∼ (10^-3) and β<inf>s</inf> ∼ (10^-4). Its implications to the test of inflationary models are also discussed.

DOI： 10.1088/1475-7516/2018/02/053

Web of Science

Scopus

arXiv

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Institute of Physics Publishing  

It has been proposed that primordial black holes (PBHs) form binaries in the radiation dominated era. Once formed, some fraction of them may merge within the age of the universe by gravitational radiation reaction. We investigate the merger rate of the PBH binaries when the PBHs have a distribution of masses around O(10)M, which is a generalization of the previous studies where the PBHs are assumed to have the same mass. After deriving a formula for the merger time probability distribution in the PBH mass plane, we evaluate it under two different approximations. We identify a quantity constructed from the mass distribution of the merger rate density per unit cosmic time and comoving volume R(m1, m2), α = -(m1+ m2)2∂2 In R/∂m1∂m2, which universally satisfies 0.97≲α≲ 1.05 for all binary masses independently of the PBH mass function. This result suggests that the measurement of this quantity is useful for testing the PBH scenario.

DOI： 10.3847/1538-4357/aaa7f4

Open Access

Scopus

arXiv

記述言語：英語   出版者・発行元：Institute of Physics Publishing  

This article reviews current understanding of primordial black holes (PBHs), with particular focus on those massive examples (≳1015 g) which remain at the present epoch, not having evaporated through Hawking radiation. With the detection of gravitational waves by LIGO, we have gained a completely novel observational tool to search for PBHs, complementary to those using electromagnetic waves. Taking the perspective that gravitational-wave astronomy will make significant progress in the coming decades, the purpose of this article is to give a comprehensive review covering a wide range of topics on PBHs. After discussing PBH formation, as well as several inflation models leading to PBH production, we summarize various existing and future observational constraints. We then present topics on formation of PBH binaries, gravitational waves from PBH binaries, and various observational tests of PBHs using gravitational waves.

DOI： 10.1088/1361-6382/aaa7b4

Open Access

Scopus

arXiv

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Monthly Notices of the Royal Astronomical Society Letters  

We provide a new bound on the amplitude of primordial magnetic fields (PMFs) by using a novel mechanism, magnetic reheating. The damping of the magnetohydrodynamics fluid motions in a primordial plasma brings the dissipation of the PMFs. In the early Universe with z ≳ 2 × 10⁶, cosmic microwave background (CMB) photons are quickly thermalized with the dissipated energy and shift to a different Planck distribution with a new temperature. In other words, the PMF dissipation changes the baryon-to-photon number ratio, and we name such a process magnetic reheating. From the current baryon-to-photon number ratio obtained from the big bang nucleosynthesis and CMB observations, we put the strongest constraint on the PMFs on small scales which CMB observations cannot access, B<inf>0</inf> ≲ 1.0 μG at the scales 10⁴ < k < 10⁸ h Mpc^-1.Moreover, when the PMF spectrum is given in a blue power-law type, the magnetic reheating puts a quite strong constraint, for example, B<inf>0</inf> ≲ 10^-17, 10^-23, and 10^-29 nG at 1 comoving Mpc for n<inf>B</inf> = 1.0, 2.0, and 3.0, respectively. This constraint would give an impact on generation mechanisms of PMFs in the early Universe.

DOI： 10.1093/mnrasl/slx195

Web of Science

Scopus

arXiv

掲載種別：研究論文（学術雑誌）   出版者・発行元：IOP Publishing  

We consider the inflationary universe with a spectator scalar field coupled
to a $U(1)$ gauge field and calculate curvature perturbation and gravitational
waves (GWs). We find that the sourced GWs can be larger than the one from
vacuum fluctuation and they are statistically anisotropic as well as linearly
polarized. The GW power spectrum acquires higher multipole moments as
$\mathcal{P}_h \propto (1-\cos^2\theta+\cos^4\theta-\cos^6\theta)$ irrespective
of the model parameters.

DOI： 10.1088/1475-7516/2018/07/023

arXiv

その他リンク： http://arxiv.org/pdf/1801.02778v1

We present an impact of coupling between dark matter and a scalar field,
which might be responsible for dark energy, on measurements of redshift-space
distortions. We point out that, in the presence of conformal and/or disformal
coupling, linearized continuity and Euler equations for total matter fluid
significantly deviate from the standard ones even in the sub-horizon scales. In
such a case, a peculiar velocity of total matter field is determined not only
by a logarithmic time derivative of its density perturbation but also by
density perturbations for both dark matter and baryon, leading to a large
modification of the physical interpretation of observed data obtained by
measurements of redshift-space distortions. We reformulate galaxy two-point
correlation function in the redshift space based on the modified continuity and
Euler equations. We conclude from the resultant formula that the true value of
the linear growth rate of large-scale structure cannot be necessarily
constrained by single-redshift measurements of the redshift-space distortions,
unless one observes the actual time-evolution of structure.

DOI： 10.1093/pasj/psy083

arXiv

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Physical Review D  

We explore the use of the galaxy bispectrum induced by the nonlinear gravitational evolution as a possible probe to test general scalar-tensor theories with second-order equations of motion. We find that time dependence of the leading second-order kernel is approximately characterized by one parameter, the second-order index, which is expected to trace the higher-order growth history of the Universe. We show that our new parameter can significantly carry new information about the nonlinear growth of structure. We forecast future constraints on the second-order index as well as the equation-of-state parameter and the growth index.

DOI： 10.1103/PhysRevD.96.123516

Web of Science

Scopus

arXiv

その他リンク： http://arxiv.org/pdf/1709.03243v1

記述言語：英語   出版者・発行元：Journal of Cosmology and Astroparticle Physics  

We revisit the generation of dark matter isocurvature perturbations in the curvaton model in greater detail, both analytically and numerically. As concrete examples, we investigate the cases of thermally decoupled dark matter and axionic dark matter. We show that the radiation produced by the decay of the curvaton, which has not been taken into account in previous analytical studies, can significantly affect the amplitude of isocurvature perturbations. In particular, we find that they are drastically suppressed even when the dark matter freeze-out (or the onset of the axion oscillations for axionic dark matter) occurs before the curvaton decays, provided the freeze-out takes place deep in the curvaton-dominated Universe. As a consequence, we show that the current observational isocurvature constraints on the curvaton parameters are not as severe as usually thought.

DOI： 10.1088/1475-7516/2017/12/042

Web of Science

Scopus

arXiv

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：OXFORD UNIV PRESS INC  

We estimate the spin distribution of primordial black holes based on the
recent study of the critical phenomena in the gravitational collapse of a
rotating radiation fluid. We find that primordial black holes are mostly slowly
rotating.

DOI： 10.1093/ptep/ptx087

Open Access

Web of Science

arXiv

その他リンク： http://arxiv.org/pdf/1704.06573v2

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER PHYSICAL SOC  

We explore the use of galaxy bispectra with multitracer technique as a
possible probe of primordial non-Gaussianities. We forecast future constraints
on non-linearity parameters, $f_{\rm NL}^{\rm eq}$ and $f_{\rm NL}^{\rm orth}$,
which respectively characterize the equilateral- and orthogonal-types
primordial bispectra, and show that the multitracer analysis would be effective
with reducing the cosmic-variance noise if the number density of galaxies is
high enough. We find that the measurement of galaxy bispectrum by future galaxy
surveys can reach the constraints on the non-local type primordial
non-Gaussianities to the level severer than current one which has been obtained
by cosmic microwave background observations.

DOI： 10.1103/PhysRevD.95.063530

Web of Science

arXiv

記述言語：英語   出版者・発行元：Monthly Notices of the Royal Astronomical Society  

We perform a Fisher analysis to estimate the expected constraints on the epoch-of-reionization (EoR) model parameters (i.e. minimum virial temperature, the ionizing efficiency and the mean free path of ionizing photons) taking into account the thermal noise of the existing telescopes, MWA and LOFAR. We consider how the inclusion of the 21-cm bispectrum improves the constraints compared to using the power spectrum alone. Assuming that we perfectly remove the foregrounds, we found that the bispectrum, which is calculated by the 21-CM FAST code, can constrain the EoR model parameters more tightly than the power spectrum since the bispectrum is more sensitive to the EoR model parameters than the power spectrum. We also found that degeneracy between the EoR model parameters can be reduced by combining the bispectrum with the power spectrum.

DOI： 10.1093/mnras/stx530

Web of Science

Scopus

arXiv

記述言語：英語   出版者・発行元：AMER PHYSICAL SOC  

We investigate expected constraints on equilateral-type primordial
non-Gaussianities from future/ongoing imaging surveys, making use of the fact
that they enhance the halo/galaxy bispectrum on large scales. As model
parameters to be constrained, in addition to $f_{\rm NL}^{\rm equil}$, which is
related to the primordial bispectrum, we consider $g_{\rm NL}^{(\partial
\sigma)^4}$, which is related to the primordial trispectrum that appeared in
the effective field theory of inflation. After calculating the angular
bispectra of the halo/galaxy clustering and weak gravitational lensing based on
the integrated perturbation theory, we perform Fisher matrix analysis for three
representative surveys. We find that among the three surveys, the tightest
constraints come from Large Synoptic Survey Telescope ; its expected $1\sigma$
errors on $f_{\rm NL}^{\rm equil}$ and $g_{\rm NL}^{(\partial \sigma)^4}$ are
respectively given by $7.0 \times 10^2$ and $4.9 \times 10^7$. Although this
constraint is somewhat looser than the one from the current cosmic microwave
background observation, since we obtain it independently, we can use this
constraint as a cross check. We also evaluate the uncertainty with our results
caused by using several approximations and discuss the possibility to obtain
tighter constraint on $f_{\rm NL}^{\rm equil}$ and $g_{\rm NL}^{(\partial
\sigma)^4}$.

DOI： 10.1103/PhysRevD.94.043532

Web of Science

arXiv

記述言語：英語   出版者・発行元：AMER PHYSICAL SOC  

The conventional slow-roll approximation is broken in the so-called "ultra
slow-roll" models of inflation, for which the inflaton potential is exactly (or
extremely) flat. The interesting nature of (canonical) ultra slow-roll
inflation is that the curvature perturbation grows on superhorizon scales, but
has a scale-invariant power spectrum. We study the ultra slow-roll inflationary
dynamics in the presence of non-canonical kinetic terms of the scalar field,
namely ultra slow-roll G-inflation. We compute the evolution of the curvature
perturbation and show that the primordial power spectrum follows a broken power
law with an oscillation feature. It is demonstrated that this could explain the
lack of large-scale power in the cosmic microwave background temperature
anisotropies. We also point out that the violation of the null energy condition
is prohibited in ultra slow-roll G-inflation and hence a blue tensor tilt is
impossible as long as inflation is driven by the potential. This statement is,
however, not true if the energy density is dominated by the kinetic energy of
the scalar field.

DOI： 10.1103/PhysRevD.94.103515

Web of Science

arXiv

記述言語：英語  

DOI： 10.1103/PhysRevLett.117.061101

Web of Science

PubMed

arXiv

記述言語：英語   出版者・発行元：Publications of the Astronomical Society of Japan  

In the past several decades, the standard cosmological model has been established and its parameters have been measured to a high precision, while there are still many fundamental questions in cosmology; such as the physics in the very early universe, the origin of the cosmic acceleration, and the nature of dark matter. The forthcoming radio telescope, the Square Kilometre Array (SKA), which will be the world's largest, will be able to open a new frontier in cosmology and will be one of the most powerful tools for cosmology in the coming decade. The cosmological surveys conducted by the SKA would have the potential not only to answer these fundamental questions but also deliver precision cosmology. In this article we briefly review the role of the SKA from the viewpoint of modern cosmology. The cosmological science led by the SKA-Japan Consortium (SKA-JP) Cosmology Science Working Group is also discussed.

DOI： 10.1093/pasj/psw098

Web of Science

Scopus

arXiv

記述言語：英語   出版者・発行元：Physical Review D  

We investigate the statistical power of higher-order statistics and cross-correlation statistics to constrain the primordial non-Gaussianity from the imaging surveys. In particular, we consider the local-type primordial non-Gaussianity and discuss how well one can tightly constrain the higher-order non-Gaussian parameters (gNL and τNL) as well as the leading-order parameter fNL from the halo/galaxy clustering and weak gravitational lensing measurements. Making use of a strong scale-dependent behavior in the galaxy/halo clustering, Fisher matrix analysis reveals that the bispectra can break the degeneracy between non-Gaussian parameters (fNL, gNL and τNL), and this will give simultaneous constraints on those three parameters. The combination of cross-correlation statistics further improves the constraints by a factor of 2. As a result, upcoming imaging surveys like the Large Synoptic Survey Telescope have the potential to improve the constraints on the primordial non-Gaussianity much tighter than those obtained from the CMB measurement by Planck, giving us an opportunity to test the single-sourced consistency relation, τNL≥(36/25)fNL2.

DOI： 10.1103/PhysRevD.93.103537

Web of Science

Scopus

arXiv

記述言語：英語   出版者・発行元：Monthly Notices of the Royal Astronomical Society  

Redshifted 21 cm signal is a promising tool to investigate the state of intergalactic medium (IGM) in the cosmic dawn (CD) and epoch of reionization (EoR). In our previous work, we studied the variance and skewness of the 21 cm fluctuations to give a clear interpretation of the 21 cm power spectrum and found that skewness is a good indicator of the epoch when X-ray heating becomes effective. Thus, the non-Gaussian feature of the spatial distribution of the 21 cm signal is expected to be useful to investigate the astrophysical effects in the CD and EoR. In this paper, in order to investigate such a non-Gaussian feature in more detail, we focus on the bispectrum of the 21 cm signal. It is expected that the 21 cm brightness temperature bispectrum is produced by non-Gaussianity due to the various astrophysical effects such as the Wouthuysen-Field effect, X-ray heating and reionization. We study the various properties of 21 cm bispectrum such as scale dependence, shape dependence and redshift evolution. And also we study the contribution from each component of 21 cm bispectrum. We find that the contribution from each component has characteristic scale-dependent feature. In particular, we find that the bulk of the 21 cm bispectrum at z = 20 comes from the matter fluctuations, while in other epochs it is mainly determined by the spin and/or neutral fraction fluctuations and it is expected that we could obtain more detailed information on the IGM in the CD and EoR by using the 21 cm bispectrum in the future experiments, combined with the power spectrum and skewness.

DOI： 10.1093/mnras/stw482

Web of Science

Scopus

arXiv

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：American Physical Society  

Primordial black holes (PBHs) are theoretical black holes which can be formed during the radiation dominant era through the gravitational collapse of radiational overdensities. It has been well known that in the context of the structure formation in our Universe such collapsed objects, e.g., halos/galaxies, could be considered as bias tracers of underlying matter fluctuations and the halo/galaxy bias has been studied well. Applying such a biased tracer picture to PBHs, we investigate the large scale clustering of PBHs and obtain an almost mass-independent constraint to the scenario that the dark matter (DM) consists of PBHs. We focus on the case where the statistics of the primordial curvature perturbations is almost Gaussian, but with small local-type non-Gaussianity. If PBHs account for the DM abundance, such a large scale clustering of PBHs behaves as nothing but the matter isocurvature perturbation which is strictly constrained by the observations of cosmic microwave backgrounds (CMBs). From this constraint, we show that, in the case where a certain single field causes both CMB temperature perturbations and PBH formation, the PBH-DM scenario is excluded even with quite small local-type non-Gaussianity, |fNL|∼O(0.01).

DOI： 10.1103/PhysRevD.91.123534

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：American Physical Society  

We investigate the effect of equilateral-type primordial trispectrum on the halo/galaxy bispectrum. We consider three types of equilateral primordial trispectra which are generated by quartic operators naturally appearing in the effective field theory of inflation and can be characterized by three nonlinearity parameters, gNLσ4, gNLσ2(∂σ)2, and gNL(∂σ)4. Recently, constraints on these parameters have been investigated from Cosmic Microwave Background (CMB) observations by using WMAP9 data. In order to consider the halo/galaxy bispectrum with the equilateral-type primordial trispectra, we adopt the integrated perturbation theory in which the effects of primordial non-Gaussianity are wholly encapsulated in the linear primordial polyspectrum for the evaluation of the biased polyspectrum. We show the shapes of the halo/galaxy bispectrum with the equilateral-type primordial trispectra and find that the primordial trispectrum characterized by gNLσ4 provides the same scale dependence as the gravity-induced halo/galaxy bispectrum. Hence, it would be difficult to obtain the constraint on gNLσ4 from the observations of the halo/galaxy bispectrum. On the other hand, the primordial trispectra characterized by gNLσ2(∂σ)2 and gNL(∂σ)4 provide the common scale dependence which is different from that of the gravity-induced halo/galaxy bispectrum on large scales. Hence, future observations of the halo/galaxy bispectrum would give constraints on the nonlinearity parameters, gNLσ2(∂σ)2 and gNL(∂σ)4 independently from CMB observations.

DOI： 10.1103/PhysRevD.91.123521

Scopus

記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：Kyoto University, Yukawa Institute for Theoretical Physics  

We consider USR k- and G-inflation driven by potential. In certain Lagrangian cases, we can construct the models which explain large scale suppression of Cl .

Scopus

記述言語：英語   出版者・発行元：IOP PUBLISHING LTD  

We calculate the CMB $\mu$-distortion and the angular power spectrum of its
cross-correlation with the temperature anisotropy in the presence of the
non-Gaussian neutrino isocurvature density (NID) mode. While the pure Gaussian
NID perturbations give merely subdominant contribution to $<\mu>$ and vanishing
$< \mu T>$, the latter quantity can be large enough to be detected in the
future when the NID perturbations $\mathcal S(\mathbf x)$ are proportional to
the square of a Gaussian field $g(\mathbf x)$, i.e. $\mathcal S({\mathbf
x})\propto g^2({\mathbf x})$. In particular, large $< \mu T>$ can be realized
since Gaussian-squared perturbations can yield a relatively large bispectrum,
satisfying the constraints from the power spectrum of CMB anisotropies, i.e.
$\mathcal{P}_\mathcal{SS}(k_0) \sim\mathcal{P}_g^2(k_0)\lesssim10^{-10}$ at
$k_0=0.05$ Mpc$^{-1}$. We also forecast constraints from the CMB temperature
and E-mode polarisation bispectra, and show that
$\mathcal{P}_g(k_0)\lesssim10^{-5}$ would be allowed from Planck data. We find
that $< \mu >$ and $|l(l+1)C^{\mu T}_l|$ can respectively be as large as
$10^{-9}$ and $10^{-14}$ with uncorrelated scale-invariant NID perturbations
for $\mathcal{P}_g(k_0)=10^{-5}$. When the spectrum of the Gaussian field is
blue-tilted (with spectral index $n_g \simeq 1.5$), $< \mu T>$ can be enhanced
by an order of magnitude.

DOI： 10.1088/1475-7516/2015/03/013

Web of Science

arXiv

記述言語：英語   出版者・発行元：Monthly Notices of the Royal Astronomical Society  

The redshifted 21cm line signal from neutral hydrogens is a promising tool to probe the cosmic dawn and the epoch of reionization. Ongoing and future low-frequency radio experiments are expected to detect its fluctuations, especially through the power spectrum. In this paper, we give a physical interpretation of the time evolution of the power spectrum of the 21cm brightness temperature fluctuations, which can be decomposed into dark matter density, spin temperature and neutral fraction of hydrogen fluctuations. From the one-point statistics of the fluctuations, such as variance and skewness, we find that the peaks and dips in the time evolution are deeply related to X-ray heating of the intergalactic gas, which controls the spin temperature. We suggest the skewness of the brightness temperature distribution is a key observable to identify the onset of X-ray heating.

DOI： 10.1093/mnras/stv965

Web of Science

Scopus

arXiv

記述言語：英語   出版者・発行元：OXFORD UNIV PRESS INC  

We consider the possibility of enhancing the inflationary tensor mode by
introducing a spectator scalar field with a small sound speed which induces
gravitational waves as a second order effect. We analytically obtain the power
spectra of gravitational waves and curvature perturbation induced by the
spectator scalar field. We found that the small sound speed amplifies the
curvature perturbation much more than the tensor mode and the current
observational constraint forces the induced gravitational waves to be
negligible compared with those from the vacuum fluctuation during inflation.

DOI： 10.1093/ptep/ptv037

Open Access

Web of Science

arXiv

その他リンク： http://arxiv.org/pdf/1411.3658v1

記述言語：英語   出版者・発行元：IOP PUBLISHING LTD  

Matter isocurvature perturbations are strictly constrained from cosmic
microwave background observations. We study a sneutrino curvaton model where
both cold dark matter (CDM)/baryon isocurvature perturbations are generated. In
our model, total matter isocurvature perturbations are reduced since the
CDM/baryon isocurvature perturbations compensate for each other. We show that
this model can not only avoid the stringent observational constraints but also
suppress temperature anisotropies on large scales, which leads to improved
agreement with observations.

DOI： 10.1088/1475-7516/2014/10/068

Open Access

Web of Science

arXiv

その他リンク： http://arxiv.org/pdf/1409.1669v1

記述言語：英語   出版者・発行元：IOP PUBLISHING LTD  

We study the impact of a temperature-dependent curvaton decay rate on the
primordial curvature perturbation generated in the curvaton scenario. Using the
familiar sudden decay approximation, we obtain an analytical expression for the
curvature perturbation after the decay of the curvaton. We then investigate
numerically the evolution of the background and of the perturbations during the
decay. We first show that the instantaneous transfer coefficient, related to
the curvaton energy fraction at the decay, can be extended into a more general
parameter, which depends on the net transfer of the curvaton energy into
radiation energy or, equivalently, on the total entropy ratio after the
complete curvaton decay. We then compute the curvature perturbation and compare
this result with the sudden decay approximation prediction.

DOI： 10.1088/1475-7516/2014/10/032

Web of Science

arXiv

記述言語：英語   出版者・発行元：IOP PUBLISHING LTD  

We investigate constraints on the spectral index of primordial gravitational
waves (GWs), paying particular attention to a blue-tilted spectrum. Such
constraints can be used to test a certain class of models of the early
Universe. We investigate observational bounds from LIGO+Virgo, pulsar timing
and big bang nucleosynthesis, taking into account the suppression of the
amplitude at high frequencies due to reheating after inflation and also
late-time entropy production. Constraints on the spectral index are presented
by changing values of parameters such as reheating temperatures and the amount
of entropy produced at late time. We also consider constraints under the
general modeling approach which can approximately describe various scenarios of
the early Universe. We show that the constraints on the blue spectral tilt
strongly depend on the underlying assumption and, in some cases, a highly
blue-tilted spectrum can still be allowed.

DOI： 10.1088/1475-7516/2015/02/003

Web of Science

arXiv

記述言語：英語   出版者・発行元：IOP PUBLISHING LTD  

We investigate the degeneracy of the isocurvature perturbations and the
primordial gravitational waves, by using recent observations of the cosmic
microwave background (CMB) reported by Planck and BICEP2 collaborations. We
show that the tension in the bound on the tensor-to-scalar ratio $r$ between
Planck and BICEP2 can be resolved by introducing the anti-correlated
isocurvature perturbations. Quantitatively, we find that with the
anti-correlated isocurvature perturbations the constraints on $r$ from Planck
alone and BICEP2 results can be consistent at 68 % C.L.

DOI： 10.1088/1475-7516/2014/08/043

Web of Science

arXiv

記述言語：英語   出版者・発行元：IOP PUBLISHING LTD  

We comprehensively explore the quadratic curvaton models in the chaotic
inflation. In the light of the BICEP2 result $r \approx 0.2$, all model
parameters and relevant observables are computed. It is found the curvaton
field value is constrained into a narrow range, $\sigma_* =
\mathcal{O}(10^{-2}$-$10^{-1})$ and the running of the spectral index is $n_s'
\gtrsim -10^{-3}$. We show that if the curvaton is added, the models are
heavily degenerated on the $n_s$ - $r$ plane. However, introducing a new plane,
the degeneracy can be resolved. To distinguish the curvaton models, precise
measurements of not only $r$ but also $n_s'$ and the tensor tilt $n_T$ are
required.

DOI： 10.1088/1475-7516/2014/09/015

Web of Science

arXiv

記述言語：英語   出版者・発行元：IOP PUBLISHING LTD  

Recently, BICEP2 has reported the large tensor-to-scalar ratio
$r=0.2^{+0.07}_{-0.05}$ from the observation of the cosmic microwave background
(CMB) B-mode at degree-scales. Since tensor modes induce not only CMB B-mode
but also the temperature fluctuations on large scales, to realize the
consistent temperature fluctuations with the Planck result we should consider
suppression of scalar perturbations on corresponding large scales. To realize
such a suppression, we consider anti-correlated iso-curvature perturbations
which could be realized in the simple curvaton model.

DOI： 10.1088/1475-7516/2014/05/046

Web of Science

arXiv

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Physical Review D Particles Fields Gravitation and Cosmology  

Although the cosmological paradigm based on cold dark matter and adiabatic, nearly scale-invariant primordial fluctuations is consistent with a wide variety of existing observations, it has yet to be sufficiently tested on scales smaller than those of massive galaxies, and various alternatives have been proposed that differ significantly in the consequent small-scale power spectrum (SSPS) of large-scale structure. Here we show that a powerful probe of the SSPS at k≳10Mpc-1 can be provided by the 21 cm forest, that is, systems of narrow absorption lines due to intervening, cold neutral hydrogen in the spectra of high-redshift background radio sources in the cosmic reionization epoch. Such features are expected to be caused predominantly by collapsed gas in starless minihalos, whose mass function can be very sensitive to the SSPS. As specific examples, we consider the effects of neutrino mass, running spectral index (RSI) and warm dark matter (WDM) on the SSPS, and evaluate the expected distribution in optical depth of 21 cm absorbers out to different redshifts. Within the current constraints on quantities such as the sum of neutrino masses -mν, running of the primordial spectral index dns/dlnk and WDM particle mass mWDM, the statistics of the 21 cm forest manifest observationally significant differences that become larger at higher redshifts. In particular, it may be possible to probe the range of mWDM≳10keV that may otherwise be difficult to access. Future observations of the 21 cm forest by the Square Kilometer Array may offer a unique and valuable probe of the SSPS, as long as radio sources such as quasars or Population III gamma-ray bursts with sufficient brightness and number exist at redshifts of z≳10-20, and the astrophysical effects of reionization and heating can be discriminated.

DOI： 10.1103/PhysRevD.90.083003

Web of Science

Scopus

arXiv

出版者・発行元：Physical Review D - Particles, Fields, Gravitation and Cosmology  

DOI： 10.1103/PhysRevD.89.043524

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）  

We derive a formula for the halo/galaxy bispectrum on the basis of the integrated perturbation theory (iPT). In addition to the gravity-induced non-Gaussianity, we consider the non-Gaussianity of the primordial curvature perturbations and investigate in detail the effect of such primordial non-Gaussianity on the large-scale halo/galaxy bispectrum. In iPT, the effects of primordial non-Gaussianity are wholly encapsulated in the linear (primordial) polyspectra, and we systematically calculate the contributions to the large-scale behaviors arising from the three types of primordial bispectrum (local, equilateral, and orthogonal types), and primordial trispectrum of the local-type non-Gaussianity. We find that the equilateral- and orthogonal-type non-Gaussianities show distinct scale-dependent behaviors which can dominate the gravity-induced non-Gaussianity at very large scales. For the local-type non-Gaussianity, higher-order loop corrections are found to give a significantly large contribution to the halo/galaxy bispectrum of the squeezed shape and eventually dominate over the other contributions on large scales. A diagrammatic approach based on the iPT helps us to systematically investigate an impact of such higher-order contributions to the large-scale halo/galaxy bispectrum. © 2014 American Physical Society.

DOI： 10.1103/PhysRevD.89.043524

Scopus

DOI： 10.1103/PhysRevD.89.043524

Web of Science

記述言語：英語   出版者・発行元：IOP PUBLISHING LTD  

Recently, there are several reports that the cosmic magnetic fields on Mpc
scale in void region is larger than $\sim 10^{-15}$G with an uncertainty of a
few orders from the current blazar observations. On the other hand, in
inflationary magnetogenesis models, additional primordial curvature
perturbations are inevitably produced from iso-curvature perturbations due to
generated electromagnetic fields. We explore such induced curvature
perturbations in a model independent way and obtained a severe upper bound for
the energy scale of inflation from the observed cosmic magnetic fields and the
observed amplitude of the curvature perturbation, as $\rho_{\rm inf}^{1/4} <
30{\rm GeV} \times (B_{\rm obs}/10^{-15}{\rm G})^{-1}$ where $B_{\rm obs}$ is
the strength of the magnetic field at present. Therefore, without a dedicated
low energy inflation model or an additional amplification of magnetic fields
after inflation, inflationary magnetogenesis on Mpc scale is generally
incompatible with CMB observations.

DOI： 10.1088/1475-7516/2014/03/013

Web of Science

arXiv

掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：Journal of Physics: Conference Series  

DOI： 10.1088/1742-6596/485/1/012023

Open Access

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Institute of Physics Publishing  

DOI： 10.1088/1475-7516/2014/05/E02

Scopus

記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：University of Tokyo, Kavli Institute for Physics and Mathematics of the Universe, KIPMU  

Scopus

記述言語：英語   出版者・発行元：AMER PHYSICAL SOC  

We derive a formula for the halo/galaxy bispectrum on the basis of the
integrated Perturbation Theory (iPT). In addition to the gravity-induced
non-Gaussianity, we consider the non-Gaussianity of the primordial curvature
perturbations, and investigate in detail the effect of such primordial
non-Gaussianity on the large-scale halo/galaxy bispectrum. In iPT, the effects
of primordial non-Gaussianity are wholly encapsulated in the linear
(primordial) polyspectra, and we systematically calculate the contributions to
the large-scale behaviors arising from the three types of primordial bispectrum
(local-, equilateral-, and orthogonal-types), and primordial trispectrum of the
local-type non-Gaussianity. We find that the equilateral- and orthogonal-type
non-Gaussianities show distinct scale-dependent behaviors which can dominate
the gravity-induced non-Gaussianity at very large scales. For the local-type
non-Gaussianity, higher-order loop corrections are found to give a
significantly large contribution to the halo/galaxy bispectrum of the squeezed
shape, and eventually dominate over the other contributions on large scales. A
diagrammatic approach based on the iPT helps us to systematically investigate
an impact of such higher-order contributions to the large-scale halo/galaxy
bispectrum.

DOI： 10.1103/PhysRevD.89.043524

Web of Science

arXiv

記述言語：英語   出版者・発行元：Physical Review D Particles Fields Gravitation and Cosmology  

We investigate the power spectrum of the distortion of the cosmic microwave background (CMB) due to the decay of the primordial magnetic fields. It is known that there are two types of the CMB distortions, so-called μ and y types, and we find that the signal of the y-type distortion becomes larger than that of the μ-type one. We also discuss cross power spectra between the CMB distortions and the CMB temperature anisotropy, which are naturally generated due to the existence of the primordial magnetic fields. We find that such cross power spectra have small amplitudes compared with the autopower spectra of the CMB distortions because of the Silk damping effect of the temperature anisotropy. We also investigate the possibility of detecting such a signal in the future CMB experiments, including not only absolutely calibrated experiments such as PIXIE but also relatively calibrated experiments such as LiteBIRD and CMBpol. © 2014 American Physical Society.

DOI： 10.1103/PhysRevD.89.063508

Web of Science

Scopus

arXiv

記述言語：英語   掲載種別：研究論文（学術雑誌）  

We compute the power spectrum ζ and non-linear parameters fNL and τNL of the curvature perturbation induced during inflation by the electromagnetic fields in the kinetic coupling model (IFF model). By using the observational result of ζ,fNL and τNL reported by the Planck collaboration, we study the constraint on the model comprehensively. Interestingly, if the single slow-rolling inflaton is responsible for the observed ζ, the constraint from τNL is most stringent. We also find a general relationship between fNL and τNL generated in this model. Even if fNL ∼ (1), a detectable τNL can be produced. © 2013 IOP Publishing Ltd and Sissa Medialab srl.

DOI： 10.1088/1475-7516/2013/09/009

Scopus

arXiv

記述言語：英語   出版者・発行元：IOP PUBLISHING LTD  

We investigate the gravitational wave background induced by the first order
scalar perturbations in the curvaton models. We consider the quadratic and
axion-like curvaton potential which can generate the blue-tilted power spectrum
of curvature perturbations on small scales and derive the maximal amount of
gravitational wave background today. We find the power spectrum of the induced
gravitational wave background has a characteristic peak at the frequency
corresponding to the scale reentering the horizon at the curvaton decay, in the
case where the curvaton does not dominate the energy density of the Universe.
We also find the enhancement of the amount of the gravitational waves in the
case where the curvaton dominates the energy density of the Universe. Such
induced gravitational waves would be detectable by the future space-based
gravitational wave detectors or pulsar timing observations.

DOI： 10.1088/1475-7516/2013/08/042

Web of Science

arXiv

記述言語：英語   出版者・発行元：IOP PUBLISHING LTD  

We discuss implications of Planck results for models with local type
non-Gaussianity. In light of the recent results of the Planck satellite, we
constrain model parameters of several representative models and give the
prediction of trispectrum, in particular, gNL. We also consider interesting
possibilities that trispectrum appears as the first signature of the
non-Gaussianities of the curvature perturbations, that is, fNL is small while
gNL can be significantly large.

DOI： 10.1088/1475-7516/2013/06/012

Web of Science

arXiv

その他リンク： http://arxiv.org/pdf/1303.5374v3

記述言語：英語   出版者・発行元：IOP PUBLISHING LTD  

We provide a general formula for calculating correlators of arbitrary
function of a Gaussian field. This work extends the standard leading-order
approximation based on the delta N formalism to the case where truncation of
the delta N at some low order does not yield the correct answer. As an
application of this formula, we investigate 2, 3 and 4-point functions of the
primordial curvature perturbation generated in the massless preheating model by
approximating the mapping between the curvature perturbation and the Gaussian
field as a sum of the many spiky normal distribution functions as suggested by
lattice calculations. We also discuss observational consequences of this case
and show that trispectrum would be a key observable to search signature of
preheating in the CMB map. It is found the forms of the curvature correlation
functions for any delta N, at the leading order in the correlator of the
Gaussian field, coincide with the standard local type ones. Within this
approximation, it is also found that the standard formula for the non-linearity
parameters given by the product of the derivatives of the e-folding number
still holds after we replace the bare e-folding number appearing in the
original delta N expansion with the one smoothed in the field space with a
Gaussian window function.

DOI： 10.1088/1475-7516/2013/06/018

Web of Science

arXiv

出版者・発行元：Monthly Notices of the Royal Astronomical Society  

Anisotropic stress perturbations induced by primordial Gaussian vector fields create non- Gaussianity in curvature perturbations.We found that such non-Gaussianity closely resembles the local-type non-Gaussianity parametrized by f<inf>NL</inf>, and generates scale-dependent bias in large-scale structures. We also found a simple relationship between the scale-dependent bias and the power spectrum of the vector fields.When the vector fields are interpreted as primordial magnetic fields, the effective f<inf>NL</inf> is shown to be always negative. The scale-dependent bias provides a new approach to probing primordial vector fields. © 2013 The Author. Published by Oxford University Press on behalf of the Royal Astronomical Society.

DOI： 10.1093/mnras/stt594

Web of Science

Scopus

arXiv

記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：Hirosaki University  

Scopus

記述言語：英語   出版者・発行元：Physical Review D Particles Fields Gravitation and Cosmology  

We analytically derive a more accurate formula for the power spectrum of the biased objects with the primordial non-Gaussianity parametrized not only by the nonlinearity parameter f<inf>NL</inf>, but also by g<inf>NL</inf> and τ<inf>NL</inf> which characterize the trispectrum of the primordial curvature perturbations. We adopt the integrated perturbation theory which was constructed in Matsubara. We discuss an inequality between f<inf>NL</inf> and τ<inf>NL</inf> in the context of the scale-dependent bias, by introducing a stochasticity parameter. We also mention higher order loop corrections in the scale dependency of the bias parameter. © 2013 American Physical Society.

DOI： 10.1103/PhysRevD.87.023525

Web of Science

Scopus

arXiv

その他リンク： http://arxiv.org/pdf/1210.2495v1

出版者・発行元：Journal of Cosmology and Astroparticle Physics  

We study temperature and polarization anisotropies of the cosmic microwave background (CMB) radiation sourced from primordial cross-bispectra between metric perturbations and vector fields, which are generated from the inflation model where an inflaton and a vector field are coupled. In case the vector field survives after the reheating, both the primordial scalar and tensor fluctuations can be enhanced by the anisotropic stress composed of the vector fields during radiation dominated era. We show that through this enhancement the primordial cross-bispectra generate not only CMB bispectra but also CMB power spectra. In general, we can expect such cross-bispectra produce the non-trivial mode-coupling signals between the scalar and tensor fluctuations. However, we explicitly show that such mode-coupling signals do not appear in CMB power spectra. Through the numerical analysis of the CMB scalar-mode power spectra, we find that although signals from these cross-bispectra are smaller than primary non-electromagnetic ones, these have some characteristic features such as negative auto-correlations of the temperature and polarization modes, respectively. On the other hand, signals from tensor modes are almost comparable to primary non-electromagnetic ones and hence the shape of observed B-mode spectrum may deviate from the prediction in the non-electromagnetic case. The above imprints may help us to judge the existence of the coupling between the scalar and vector fields in the early Universe. © 2012 IOP Publishing Ltd and Sissa Medialab srl.

DOI： 10.1088/1475-7516/2012/11/046

Web of Science

Scopus

arXiv

出版者・発行元：Progress of Theoretical and Experimental Physics  

We compute the full bispectra, namely both auto and cross bispectra, of primordial curvature and tensor perturbations in the most general single-field inflation model whose scalar and gravitational equations of motion are of second order. The formulae in the limits of k-inflation and potential-driven inflation are also given. These expressions are useful for estimating the full bispectra of temperature and polarization anisotropies of the cosmic microwave background radiation. © The Author(s) 2013.

DOI： 10.1093/PTEP/PTT031

Open Access

Web of Science

Scopus

arXiv

掲載種別：研究論文（学術雑誌）  

DOI： 10.1143/PTP.127.591

Scopus

出版者・発行元：Journal of Cosmology and Astroparticle Physics  

We investigate bounds on the strength of the primordial magnetic field (PMF) from the cosmic microwave background (CMB) bispectra of the intensity (temperature) modes induced from the auto- and cross-correlated bispectra of the scalar and tensor components of the PMF anisotropic stress. At first, we construct a general formula for the CMB intensity and polarization bispectra from PMFs composed of any type of perturbation. Then we derive an approximate expression which traces the exact shape of the CMB bispectrum in order to reduce the computation time with respect to a large number of the multipole configurations, and also show that the non-Gaussian structure coming from PMFs is classified as the local-type configuration. Computing the signal-to-noise ratio on the basis of the approximate formula with the information of the instrumental noises and resolutions, we find expected upper bounds on the magnetic field strength, when the magnetic spectrum is nearly scale invariant (n<inf>B</inf> = -2.9), smoothed on 1Mpc scale at 95% confidence level from the WMAP and PLANCK experiments as B<inf>1Mpc</inf> < 4.0-6.7nG and 3.8-6.5nG, respectively, depending on the energy scale of the magnetic field production from 10¹⁴GeV to 10³GeV. Our new consequences imply slight overestimations by the previous rough discussions.©2012 IOP Publishing Ltd and Sissa Medialab srl.

DOI： 10.1088/1475-7516/2012/03/041

Web of Science

Scopus

arXiv

記述言語：英語  

DOI： 10.1143/PTP.126.923

Web of Science

DOI： 10.1143/PTP.126.937

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Progress of Theoretical Physics  

We investigate the cosmic microwave background (CMB) bispectra of the intensity (temperature) and polarization modes induced by the graviton non-Gaussianities, which arise from the parity-conserving and parity-violating Weyl cubic terms with time-dependent coupling. By considering the time-dependent coupling, we find that even in the exact de Sitter space time, the parity violation still appears in the three-point function of the primordial gravitational waves and could become large. Through the estimation of the CMB bispectra, we demonstrate that the signals generated from the parity-conserving and parity-violating terms appear in completely different configurations of multipoles. For example, the parity-conserving non-Gaussianity induces the nonzero CMB temperature bispectrum in the configuration with Σ_<n=1>^3l_n=even and, while due to the parity-violating non-Gaussianity, the CMB temperature bispectrum also appears for Σ_<n=1>^3l_n=odd. This signal is just good evidence of the parity violation in the non-Gaussianity of primordial gravitational waves. We find that the shape of this non-Gaussianity is similar to the so-called equilateral one and the amplitudes of these spectra at large scale are roughly estimated as |b_<lll>|～l^<-4>×3.2×10^<-2>(GeV/Λ)^2 (r/0.1)^4, where Λ is an energy scale that sets the magnitude of the Weyl cubic terms (higher derivative corrections) and r is a tensor-to-scalar ratio. Taking the limit for the nonlinearity parameter of the equilateral type as f_<NL>^<eq><300, we can obtain a bound as Λ&gsum;3×10^6GeV, assuming r=0.1.

DOI： 10.1143/PTP.126.937

Scopus

CiNii Research

arXiv

出版者・発行元：Publication Office, Progress of Theoretical Physics  

We discuss generation of non-Gaussianity in primordial density perturbation through the super-horizon evolution during inflation by using the so-called δN formalism. In order to discuss the difficulties of generating large local-type non-Gaussianity during inflation, we discuss Kadota-Stewart model. This model gives an example in which we have to choose rather unnatural initial conditions even if large non-Gaussianity can be generated.

DOI： 10.1143/PTPS.190.135

CiNii Research

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Monthly Notices of the Royal Astronomical Society Letters  

We study the scale-dependent bias of the halo power spectrum arising from primordial non-Gaussianity. We present an analytic result of the halo bias including up to the trispectrum contributions. We find that the scale-dependent bias opens a new possibility of probing the relation between the non-linearity parametersf<inf>NL</inf> and τ<inf>NL</inf>. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS.

DOI： 10.1111/j.1745-3933.2011.01124.x

Web of Science

Scopus

記述言語：英語   出版者・発行元：Journal of Cosmology and Astroparticle Physics  

We investigate the halo bias in the case where the primordial curvature fluctuations, Φ, are sourced from both a Gaussian random field and a Gaussian-squared field, as Φ(x) = φ(x)+ψ(x)²-ψ(x) ²ngle, so-called "ungaussiton model". We employ the peak-background split formula and find a new scale-dependence in the halo bias induced from the Gaussian-squared field. © 2011 IOP Publishing Ltd and SISSA.

DOI： 10.1088/1475-7516/2011/11/001

Web of Science

Scopus

arXiv

その他リンク： http://arxiv.org/pdf/1108.5569v1

出版者・発行元：Progress of Theoretical Physics  

We investigate a statistical anisotropy on the Cosmic Microwave Background (CMB) bispectrum, which can be generated from the primordial non-Gaussianity induced by quantum fluctuations of a vector field. We find new configurations in the multipole space of the CMB bispectrum given by l_1=l_2+l_3+2,|l_2-l_3|-2 and their permutations, which violate the rotational invariance, such as an off-diagonal configuration in the CMB power spectrum. We also find that in a model presented by Yokoyama and Soda (2008), the amplitude of the statistically anisotropic bispectrum in the above configurations becomes as large as that in other configurations such as l_1=l_2+l_3. As a result, it might be possible to detect these contributions in future experiments, which would give us novel information about the physics of the early Universe.

DOI： 10.1143/PTP.126.923

Web of Science

Scopus

CiNii Research

arXiv

記述言語：英語   出版者・発行元：Journal of Cosmology and Astroparticle Physics  

For the local-type primordial perturbation, it is known that there is an inequality between the bispectrum and the trispectrum. By using the diagrammatic method, we develop a general formalism to systematically construct the similar inequalities up to any order correlation function. As an application, we explicitly derive all the inequalities up to six and eight-point functions. © 2011 IOP Publishing Ltd and SISSA.

DOI： 10.1088/1475-7516/2011/07/033

Web of Science

Scopus

arXiv

その他リンク： http://arxiv.org/pdf/1105.5851v2

記述言語：英語   出版者・発行元：Journal of Cosmology and Astroparticle Physics  

A possible origin of the anomalous dip and bump in the primordial power spectrum, which are reconstructed from WMAP data corresponding to the multipole ℓ = 100 ∼ 140 by using the inversion method, is investigated as a consequence of modification of scalar field dynamics in the inflation era. Utilizing an analytic formula to handle higher order corrections to the slow-roll approximation, we evaluate the relation between a detailed shape of inflaton potential and a fine structure in the primordial power spectrum. We conclude that it is unlikely to generate the observed dip and bump in the power spectrum by adding realistic features in the inflaton potential. In order to generate the fine structure, we find that the slow-roll parameters have to become about (100) and the number of oscillations in the potential is about (10 ²), on the scale of the structure. ©2011 IOP Publishing Ltd and SISSA.

DOI： 10.1088/1475-7516/2011/12/008

Web of Science

Scopus

arXiv

DOI： 10.1143/PTP.125.795

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Physical Review D Particles Fields Gravitation and Cosmology  

If the seed magnetic fields exist in the early Universe, tensor components of their anisotropic stresses are not compensated prior to neutrino decoupling, and the tensor metric perturbations generated from them survive passively. Consequently, due to the decay of these metric perturbations after recombination, the so-called integrated Sachs-Wolfe effect, the large-scale fluctuations of CMB radiation are significantly boosted. This kind of CMB anisotropy is called the "tensor passive mode." Because these fluctuations deviate largely from the Gaussian statistics due to the quadratic dependence on the strength of the Gaussian magnetic field, not only the power spectrum but also the higher-order correlations have reasonable signals. With these motives, we compute the CMB bispectrum induced by this mode. When the magnetic spectrum obeys a nearly scale-invariant shape, we obtain an estimation of a typical value of the normalized reduced bispectrum as <inf>1</inf>( <inf>1</inf>+1)<inf>3</inf>(<inf>3</inf>+1)|b<inf>12</inf> <inf>3</inf>|∼(130-6)×10^-16(B<inf>1Mpc</inf>/4.7nG) <inf>6</inf>, depending on the energy scale of the magnetic field production from 1014GeV to 103GeV. Here, B<inf>1Mpc</inf> is the strength of the primordial magnetic field smoothed on 1 Mpc. From the above estimation and the current observational constraint on the primordial non-Gaussianity, we get a rough constraint on the magnetic field strength as B<inf>1Mpc</inf><2.6-4.4nG. © 2011 American Physical Society.

DOI： 10.1103/PhysRevD.83.123003

Web of Science

Scopus

arXiv

記述言語：英語   出版者・発行元：Monthly Notices of the Royal Astronomical Society  

We study the halo mass function in the presence of a kurtosis type of primordial non-Gaussianity. The kurtosis corresponds to the trispectrum as defined in Fourier space. The primordial trispectrum is commonly characterized by two parameters, τ<inf>NL</inf> and g<inf>NL</inf>. We focus on τ<inf>NL</inf> which is an important parameter to test the physics of multifield inflation models. As applications of the derived non-Gaussian mass function, we consider the effects on the abundance of void structure, on early star formation and on formation of the most massive objects at high redshift. We show that by comparing the effects of primordial non-Gaussianity on cluster abundance with that on void abundance, we can distinguish between the skewness and the kurtosis types of primordial non-Gaussianity. As for early star formation, we show that the kurtosis type of primordial non-Gaussianity seems on the average not to affect the reionization history of the Universe. However, at high redshifts (up to z≃ 20) such non-Gaussianity does somewhat affect the early stages of reionization. © 2011 The Authors. Monthly Notices of the Royal Astronomical Society © 2011 RAS.

DOI： 10.1111/j.1365-2966.2011.19323.x

Web of Science

Scopus

arXiv

出版者・発行元：Physical Review D Particles Fields Gravitation and Cosmology  

We present a detailed calculation of our previous short paper in which we have investigated a constraint on the magnetic field strength through comic microwave background temperature bispectrum of vector modes induced from primordial magnetic fields. By taking into account full angular dependence of the bispectrum with spin spherical harmonics and Wigner symbols, we explicitly show that the cosmic microwave background bispectrum induced from the statistical-isotropic primordial vector fluctuations can be also described as an angle-averaged form in the rotationally invariant way. We also study the cases with different spectral indices of the power spectrum of the primordial magnetic fields. © 2011 American Physical Society.

DOI： 10.1103/PhysRevD.83.123523

Web of Science

Scopus

arXiv

DOI： 10.1143/PTP.190.135

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1103/PHYSREVD.83.029901

Web of Science

記述言語：英語  

DOI： 10.1143/PTP.190.135

掲載種別：研究論文（学術雑誌）   出版者・発行元：Physical Review D Particles Fields Gravitation and Cosmology  

We calculate the cosmic microwave background bispectrum of vector modes induced from primordial magnetic fields. We take into account the full angular dependence of the bispectrum and discuss the amplitude and also the shape of the bispectrum in ? space. In the squeezed limit as ?<inf>1</inf>=? <inf>2</inf>-<inf>3</inf>, we estimate a typical values of the normalized reduced bispectrum as ?<inf>1</inf>(?<inf>1</inf>+1)?<inf>3</inf>(? <inf>3</inf>+1)b<inf>?1</inf>?<inf>2</inf>?<inf>3</inf>∼2× 10⊃-19, for the strength of the primordial magnetic field smoothed on 1 Mpc scale B<inf>1Mpc</inf>=4.7nG assuming a nearly scale-invariant spectrum of magnetic fields. We find that a constraint on the magnetic field strength will be roughly estimated as B<inf>1Mpc</inf><10nG, if PLANCK places a limit on the nonlinearity parameter of local-type configuration as fNLlocal<5. © 2010 The American Physical Society.

DOI： 10.1103/PhysRevD.82.121302

Web of Science

Scopus

出版者・発行元：Progress of Theoretical Physics  

We present an all-sky formalism for the Cosmic Microwave Background (CMB) bispectrum induced by the primordial non-Gaussianities not only in scalar but also in vector and tensor fluctuations. We find that the bispectrum can be formed in an explicitly rationally invariant way by taking into account the angular and polarization dependences of the vector and tensor modes. To demonstrate this and present how to use our formalism, we consider a specific example of the correlation between two scalars and a graviton as the source of non-Gaussianity. As a result, we show that the CMB reduced bispectrum of the intensity anisotropies is evaluated as a function of the multipole and the coupling constant between two scalars and a graviton denoted by g_<tss>; |b_<lll>|～l^<-4>×8×10^<-18>|g_<tss>|. By estimating the signal-to-noise ratio, we find that the constraint as |g_<tss>|<6 will be expected from the PLANCK experiment.

DOI： 10.1143/PTP.125.795

Web of Science

Scopus

CiNii Research

arXiv

出版者・発行元：Proceedings of the 20th Workshop on General Relativity and Gravitation in Japan, JGRG 2010  

Scopus

記述言語：英語   出版者・発行元：Journal of Cosmology and Astroparticle Physics  

We classify models generating large local-type non-Gaussianity into some categories by using some "consistency relations" among the non-linearity parameters f<inf>nl</inf>^localτ<inf>nL</inf> ^local and g<inf>NL</inf>^local, which characterize the size of bispectrum for the former and trispectrum for the latter two. Then we discuss how one can discriminate models of large local-type non-Gaussianity with such relations. We first classify the models by using the ratio of T <inf>NL</inf>^local/(6f<inf>NL</inf>^local/5)², which is unity for "single-source" models and deviates from unity for "multi-source" ones. We can make a further classification of models in each category by utilizing the relation between f<inf>NL</inf>^local and G<inf>nl</inf>^local. Our classification suggests that observations of trispectrum would be very helpful to distinguish models of large non-Gaussianity and may reveal the generation mechanism of primordial fluctuations. © 2010 IOP Publishing Ltd and SISSA.

DOI： 10.1088/1475-7516/2010/12/030

Web of Science

Scopus

arXiv

記述言語：英語   出版者・発行元：Journal of Cosmology and Astroparticle Physics  

Modulated reheating scenario is one of the most attractive models that predict possible detections of not only the primordial non-Gaussianity but also the tensor fluctuation through future CMB observations such as the Planck satellite, the PolarBeaR and the LiteBIRD satellite experiments. We study the baryonic-isocurvature fluctuations in the Affleck-Dine baryogenesis with the modulated reheating scenario. We show that the Affleck- Dine baryogenesis can be consistent with the modulated reheating scenario with respect to the current observational constraint on the baryonic-isocurvature fluctuations. © 2011 IOP Publishing Ltd and SISSA.

DOI： 10.1088/1475-7516/2011/01/027

Web of Science

Scopus

arXiv

その他リンク： http://arxiv.org/pdf/1008.1450v2

記述言語：英語   出版者・発行元：Physical Review Letters  

We show that current cosmic acceleration can be explained by an almost massless scalar field experiencing quantum fluctuations during primordial inflation. Provided its mass does not exceed the Hubble parameter today, this field has been frozen during the cosmological ages to start dominating the Universe only recently. By using supernovae data, completed with baryonic acoustic oscillations from galaxy surveys and cosmic microwave background anisotropies, we infer the energy scale of primordial inflation to be around a few TeV, which implies a negligible tensor-to-scalar ratio of the primordial fluctuations. Moreover, our model suggests that inflation lasted for an extremely long period. Dark energy could therefore be a natural consequence of cosmic inflation close to the electroweak energy scale. © 2010 The American Physical Society.

DOI： 10.1103/PhysRevLett.105.121301

Web of Science

Scopus

PubMed

arXiv

記述言語：英語  

DOI： 10.1088/0264-9381/27/12/124003

Web of Science

arXiv

出版者・発行元：Physical Review D Particles Fields Gravitation and Cosmology  

We present a complete set of formulae for calculating the bispectra of CMB temperature and polarization anisotropies generated from non-Gaussianity in the vector and tensor mode perturbations. In the all-sky analysis, it is found that the bispectrum formulae for the tensor and vector-mode non-Gaussianity formally take complicated forms compared to the scalar mode one because the photon transfer functions in the tensor and vector modes depend on the azimuthal angle between the direction of the wave number vector of the photon's perturbation and that of the line of sight. We demonstrate that flat-sky approximations remove this difficulty because this kind of azimuthal angle dependence apparently vanishes in the flat-sky limit. Through the flat-sky analysis, we also find that the vector or tensor bispectrum of B-mode polarization vanishes in the squeezed limit, unless the cosmological parity is violated at the nonlinear level. © 2010 The American Physical Society.

DOI： 10.1103/PhysRevD.82.103505

Web of Science

Scopus

arXiv

記述言語：英語   出版者・発行元：Journal of Cosmology and Astroparticle Physics  

We revisit ghost dark matter, the possibility that ghost condensation may serve as an alternative to dark matter. In particular, we investigate the Friedmann-Robertson-Walker (FRW) background evolution and the large-scale structure (LSS) in the ΛGDM universe, i.e. a late-time universe dominated by a cosmological constant and ghost dark matter. The FRW background of the ΛGDM universe is indistinguishable from that of the standard ΛCDM universe if M ≳ 1eV, where M is the scale of spontaneous Lorentz breaking. From the LSS we find a stronger bound: M ≳ 10eV. For smaller M, ghost dark matter would have non-negligible sound speed after the matter-radiation equality, and thus the matter power spectrum would significantly differ from observation. These bounds are compatible with the phenomenological upper bound M ≲ 100GeV known in the literature. © 2010 IOP Publishing Ltd and SISSA.

DOI： 10.1088/1475-7516/2010/05/007

Web of Science

Scopus

arXiv

記述言語：英語   出版者・発行元：Journal of Physics: Conference Series  

In this talk, we have shown that current cosmic acceleration can be explained by an almost massless scalar field experiencing quantum fluctuations during primordial inflation. Provided its mass does not exceed the Hubble parameter today, this field has been frozen during the cosmological ages to start dominating the universe only recently. By using supernovae data, completed with baryonic acoustic oscillations from galaxy surveys and cosmic microwave background anisotropies, we infer the energy scale of primordial inflation to be around a few TeV, which implies a negligible tensor-to-scalar ratio of the primordial fluctuations. Moreover, our model suggests that inflation lasted for an extremely long period. Dark energy could therefore be a natural consequence of cosmic inflation close to the electroweak energy scale. © 2010 IOP Publishing Ltd.

DOI： 10.1088/1742-6596/259/1/012082

Open Access

Web of Science

Scopus

掲載種別：研究論文（国際会議プロシーディングス）  

We calculate CMB bispectrum of vector modes induced from primordial magnetic fields. We take into account the full angular dependence of the bispectrum and discuss the amplitude and also the shape of the bispectrum. In the squeezed limit, we estimate a typical values of the normalized reduced bispectrum as ℓ11(ℓ1+1) ℓ3(ℓ 3+1) |bℓ1ℓ2ℓ3|∼2 × 10 -19, for the strength of the primordial magnetic field smoothed on 1Mpc scale B1Mpc = 4.7nG assuming nearly scale-invariant spectrum of magnetic fields. We find that a new constraint on the magnetic field strength will be placed as B1Mpc < 10nG if PLANCK will place a limit on the nonlinearity parameter of local-type configuration as |flocalNL | < 5.

Scopus

記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：Proceedings of the 20th Workshop on General Relativity and Gravitation in Japan Jgrg 2010  

Modulated reheating scenario is one of the most attractive models that predict possible detections of primordial non-Gaussianity through future CMB observations such as the Planck satellite. We study the baryonic-isocurvature fluctuations in the Affleck- Dine baryogenesis with the modulated reheating scenario. We show that the simple Affleck-Dine baryogenesis would be incompatible with the modulated reheating scenario with respect to the current observational constraint on the baryonic-isocurvature fluctuations, like a gravitino dark matter scenario.

Scopus

記述言語：英語   出版者・発行元：Journal of Cosmology and Astroparticle Physics  

We consider primordial fluctuations in thermal inflation scenario. Since the thermal inflation drives about 10 e-folds after the standard inflation, the time of horizon-exit during inflation corresponding to the present observational scale shifts toward the end of inflation. It generally makes the primordial power spectrum more deviated from a scale-invariant one and hence renders some models inconsistent with observations. We present a mechanism of generating the primordial curvature perturbation at the end of thermal inflation utilizing a fluctuating coupling of a flaton field with the fields in thermal bath. We show that, by adopting the mechanism, some inflation models can be liberated even in the presence of the thermal inflation. We also discuss non-Gaussianity in the mechanism and show that large non-Gaussianity can be generated in this scenario. © 2009 IOP Publishing Ltd and SISSA.

DOI： 10.1088/1475-7516/2009/12/012

Web of Science

Scopus

arXiv

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Physical Review D Particles Fields Gravitation and Cosmology  

We investigate primordial non-Gaussianity and dark matter isocurvature fluctuations in the modulated reheating and the curvaton scenarios. In these scenarios, a large non-Gaussianity can be generated; on the other hand, depending on how dark matter is produced, too large isocurvature fluctuations can also arise, which is inconsistent with current observations. In this paper, we study this issue in a mixed scenario where the curvature fluctuations can also be produced from the inflaton fluctuations as well as those from a light scalar field such as the modulus and the curvaton. We show that primordial fluctuations can be highly non-Gaussian without conflicting with the current constraint on isocurvature fluctuations for such mixed scenarios. However, if the constraint on isocurvature fluctuations becomes severer as expected by the Planck satellite, fNL, a nonlinearity parameter for adiabatic fluctuations, should be very small as fNL3, which would give interesting implications for the generation mechanism of dark matter. Non-Gaussianity from isocurvature fluctuations is also discussed in these scenarios. © 2009 The American Physical Society.

DOI： 10.1103/PhysRevD.80.063524

Web of Science

Scopus

記述言語：英語   出版者・発行元：Physics Letters Section B Nuclear Elementary Particle and High Energy Physics  

We investigate density fluctuations in a scenario with gravitino dark matter in the framework of modulated reheating, which is known to generate large non-Gaussianity. We show that gravitino dark matter is disfavored in this framework. We also briefly discuss the case with the curvaton mechanism and some other possible dark matter scenarios. © 2009 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physletb.2009.06.007

Web of Science

Scopus

arXiv

その他リンク： http://arxiv.org/pdf/0905.0240v2

記述言語：英語   出版者・発行元：Physics Letters Section B Nuclear Elementary Particle and High Energy Physics  

We show that, assuming the dispersion relation proposed recently by Hořava in the context of quantum gravity, radiation energy density exhibits a peculiar dependence on the scale factor; the radiation energy density decreases proportional to a^-6. This simple scaling can have an impact on cosmology. As an example, we show that the resultant baryon asymmetry as well as the stochastic gravity waves can be enhanced. We also discuss current observational constraint on the dispersion relation. © 2009 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physletb.2009.07.005

Web of Science

Scopus

arXiv

その他リンク： http://arxiv.org/pdf/0905.0055v2

記述言語：英語   出版者・発行元：Journal of Cosmology and Astroparticle Physics  

Recently it was shown that an inflationary background can be realized by any p-form field non-minimally coupled to gravity. In this paper, we study gravitational waves generated during p-form inflation. Even though the background evolution is identical to that in conventional scalar field inflation, the behavior of gravitational waves is different in p-form inflation. In particular, we find that the propagation speed of gravitational waves differs from unity in 2- and 3-form inflationary models. We point out that the squared speed becomes negative in the large field models. The small field models are free from pathologies and the correction to the spectrum of gravitational waves turns out to be very small. © 2009 IOP Publishing Ltd and SISSA.

DOI： 10.1088/1475-7516/2009/05/004

Web of Science

Scopus

arXiv

記述言語：英語   出版者・発行元：Journal of Cosmology and Astroparticle Physics  

We present a new efficient method for computing the non-linearity parameters of the higher order correlation functions of local type curvature perturbations in inflation models having a -component scalar field, focusing on the non-Gaussianity generated during the evolution on super-horizon scales. In contrast to the naive expectation that the number of operations necessary to compute the n-point functions is proportional to ⁿ, it grows only linearly in in our formalism. Hence, our formalism is particularly powerful for the inflation models composed of a multi-component scalar field, including the models in which the slow-roll conditions are violated after the horizon crossing time. Explicit formulas obtained by applying our method are provided for n = 2, 3, 4 and 5, which correspond to power-, bi-, tri- and quad-spectra, respectively. We also discuss how many parameters we need to parameterize the amplitude and the shape of the higher order correlation functions of local type. © 2009 IOP Publishing Ltd and SISSA.

DOI： 10.1088/1475-7516/2009/02/012

Web of Science

Scopus

arXiv

記述言語：英語   出版者・発行元：Journal of Cosmology and Astroparticle Physics  

We study an inflationary scenario with a vector impurity. We show that the universe undergoes anisotropic inflationary expansion due to a preferred direction determined by the vector. Using the slow roll approximation, we find a formula for determining the anisotropy of the inflationary universe. We discuss possible observable predictions of this scenario. In particular, it is stressed that primordial gravitational waves can be induced from curvature perturbations. Hence, even in low scale inflation, a sizable amount of primordial gravitational waves may be produced during inflation. © 2008 IOP Publishing Ltd. and SISSA.

DOI： 10.1088/1475-7516/2008/08/034

Web of Science

Scopus

arXiv

記述言語：英語   出版者・発行元：Journal of Cosmology and Astroparticle Physics  

We present a new mechanism for generating primordial statistical anisotropy of curvature perturbations. We introduce a vector field which has a non-minimal kinetic term and couples with a waterfall field in a hybrid inflation model. In such a system, the vector field gives fluctuations of the end of inflation and hence induces a subcomponent of curvature perturbations. Since the vector has a preferred direction, the statistical anisotropy could appear in the fluctuations. We present the explicit formula for the statistical anisotropy in the primordial power spectrum and the bispectrum of curvature perturbations. Interestingly, there is the possibility that the statistical anisotropy does not appear in the power spectrum but does appear in the bispectrum. We also find that the statistical anisotropy provides the shape dependence to the bispectrum. © 2008 IOP Publishing Ltd. and SISSA.

DOI： 10.1088/1475-7516/2008/08/005

Web of Science

Scopus

arXiv

記述言語：英語   出版者・発行元：AMER PHYSICAL SOC  

We give a concise formula for the non-Gaussianity of the primordial curvature
perturbation generated on super-horizon scales in multi-scalar inflation model
without assuming slow-roll conditions. This is an extension of our previous
work. Using this formula, we study the generation of non-Gaussianity for the
double inflation models in which the slow-roll conditions are temporarily
violated after horizon exit, and we show that the non-linear parameter $f_{NL}$
for such models is suppressed by the slow-roll parameters evaluated at the time
of horizon exit.

DOI： 10.1103/PhysRevD.77.083511

Web of Science

arXiv

その他リンク： http://arxiv.org/pdf/0711.2920v3

記述言語：英語   出版者・発行元：IOP PUBLISHING LTD  

We analyze the non-Gaussianity for primordial curvature perturbations
generated in multi-scalar slow-roll inflation model including the model with
non-separable potential by making use of $\delta N$ formalism. Many authors
have investigated the possibility of large non-Gaussianity for the models with
separable potential, and they have found that the non-linear parameter,
$f_{NL}$, is suppressed by the slow-roll parameters. We show that for the
non-separable models $f_{NL}$ is given by the product of a factor which is
suppressed by the slow-roll parameters and a possible enhancement factor which
is given by exponentials of quantities of O(1).

DOI： 10.1088/1475-7516/2007/07/013

Web of Science

arXiv

その他リンク： http://arxiv.org/pdf/0705.3178v1

記述言語：英語  

We show that the primordial curvature perturbations may originate not from
the quantum fluctuations of inflaton during inflation but from isocurvature
perturbations which are amplified during preheating after inflation. We
consider a simple preheating model, whose potential is given by $V(\phi,
\chi)={1/4}\lambda \phi^4+{1/2}g^2 \phi^2 \chi^2$ with $g^2/\lambda=2$, as a
possible realization of generating curvature perturbations during preheating.
We make use of the $\delta N$ formalism which requires only knowledge of the
homogeneous background solutions in order to evaluate the evolution of
curvature perturbations on super-horizon scales. We solve the background
equations numerically and find that the amplitude and the spectral index of
curvature perturbations originating from preheating can be tuned to the
observed values if the isocurvature perturbations at the end of inflation is
not suppressed on super-horizon scales. We also point out that the tensor to
scalar ratio in ${1/4}\lambda \phi^4$ inflation model can be significantly
lowered, hence letting the ${1/4}\lambda \phi^4$ model, which is ruled out by
the Wilkinson Microwave Anisotropy Probe (WMAP) data combined with SDSS data,
get back into the observationally allowed region.

DOI： 10.1088/0264-9381/24/6/015

arXiv

その他リンク： http://arxiv.org/pdf/astro-ph/0606228v2

記述言語：英語   出版者・発行元：IOP PUBLISHING LTD  

We present a new formulation for the evaluation of the primordial spectrum of
curvature perturbations generated during inflation, using the fact that the
Wronskian of the scalar field perturbation equation is constant. In the
literature, there are many works on the same issue focusing on a few specific
aspects or effects. Here we deal with the general multi-component scalar field,
and show that our new formalism gives a method to evaluate the final amplitude
of the curvature perturbation systematically and economically. The advantage of
the new method is that one only has to solve a single mode of the scalar field
perturbation equation backward in time from the end of inflation to the stage
at which the perturbation is within the Hubble horizon, at which the initial
values of the scalar field perturbations are given. We also clarify the
relation of the new method with the new delta N formalism recently developed in
Lee et al.(2005).

DOI： 10.1088/1475-7516/2006/06/020

Web of Science

arXiv

その他リンク： http://arxiv.org/pdf/astro-ph/0605021v2

記述言語：英語   出版者・発行元：IOP PUBLISHING LTD  

The delta N formula that relates the final curvature perturbation on comoving
slices to the inflaton perturbation on flat slices after horizon crossing is a
powerful and intuitive tool to compute the curvature perturbation spectrum from
inflation. However, it is customarily assumed further that the conventional
slow-roll condition is satisfied, and satisfied by all components, during
horizon crossing. In this paper, we develop a new delta N formalism for
multi-component inflation that can be applied in the most general situations.
This allows us to generalize the idea of general slow-roll inflation to the
multi-component case, in particular only applying the general slow-roll
condition to the relevant component. We compute the power spectrum of the
curvature perturbation in multi-component general slow-roll inflation, and find
that under quite general conditions it is invertible.

DOI： 10.1088/1475-7516/2005/10/004

Web of Science

arXiv

その他リンク： http://arxiv.org/pdf/astro-ph/0506262v2

記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

We reformulate the evaluation of the initial spectrum of curvature perturbations generated during multi-scalar Inflation. We point out that we can easily and sys- Tematically construct a unified formulation by using the fact that the Wronskian is constant.

Scopus

J-GLOBAL

J-GLOBAL

開催年月日： 2023年2月

記述言語：英語   会議種別：口頭発表（招待・特別）  

開催地：Seoul, Korea   国名：大韓民国  

開催年月日： 2022年12月

記述言語：英語   会議種別：口頭発表（基調）  

開催地：online  

開催年月日： 2022年9月

記述言語：日本語   会議種別：口頭発表（一般）  

開催年月日： 2022年7月

記述言語：英語   会議種別：口頭発表（招待・特別）  

開催年月日： 2025年10月

記述言語：日本語   会議種別：口頭発表（一般）  

開催年月日： 2023年10月

記述言語：日本語   会議種別：口頭発表（招待・特別）  

開催地：名古屋大学+オンライン   国名：日本国  

開催年月日： 2023年3月

記述言語：英語   会議種別：口頭発表（招待・特別）  

国名：日本国  

開催年月日： 2022年2月

記述言語：日本語   会議種別：口頭発表（招待・特別）  

開催地：online+東京  

開催年月日： 2020年11月

記述言語：英語   会議種別：ポスター発表  

国名：日本国