2023/04/12 更新

写真a

タダ ユウイチロウ
多田 祐一郎
TADA Yuichiro
所属
高等研究院 特任助教
大学院理学研究科 特任助教
職名
特任助教
連絡先
メールアドレス
外部リンク

学位 1

  1. 博士(理学) ( 2017年3月   東京大学 ) 

研究キーワード 4

  1. 初期宇宙

  2. インフレーション

  3. 原始ブラックホール

  4. 重力波

研究分野 1

  1. 自然科学一般 / 素粒子、原子核、宇宙線、宇宙物理にする理論

経歴 7

  1. 高エネルギー加速器研究機構   素粒子原子核研究所   協力研究員

    2022年4月 - 現在

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    国名:日本国

  2. 名古屋大学   高等研究院   特任助教

    2021年4月 - 現在

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    国名:日本国

  3. 大同大学   非常勤講師

    2019年4月 - 2021年3月

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    国名:日本国

    備考:力学1, 2

  4. 名古屋大学   宇宙論研究室   日本学術振興会特別研究員 PD

    2018年4月 - 2021年3月

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    国名:日本国

  5. Institute d'Astrophysique de Paris   Dr. Sébastien Renaux-Petel's Group   PD researcher

    2017年4月 - 2018年3月

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    国名:フランス共和国

  6. 東京大学   カブリ数物連携宇宙研究機構, 宇宙線研究所   日本学術振興会特別研究員 DC2

    2015年4月 - 2017年3月

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    国名:日本国

  7. 東京大学   カブリ数物連携宇宙研究機構, 宇宙線研究所   フォトンサイエンス・リーディング大学院

    2012年10月 - 2017年3月

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    国名:日本国

▼全件表示

学歴 3

  1. 東京大学   大学院理学系研究科

    2014年4月 - 2017年3月

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    国名: 日本国

    備考: 博士課程

  2. 東京大学   大学院理学系研究科

    2012年4月 - 2014年3月

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    国名: 日本国

    備考: 修士課程

  3. 東京大学   理学部   物理学科

    2008年4月 - 2012年3月

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    国名: 日本国

所属学協会 1

  1. 日本物理学会

    2013年6月 - 現在

受賞 3

  1. Outstanding Presentation Award Gold Prize

    2020年11月   Online JGRG workshop 2020   Manifestly covariant theory of stochastic inflation

  2. EPL's Highlights 2020

    Conformal inflation in the metric-affine geometry

    Yusuke Mikura, Yuichiro Tada, Shuichiro Yokoyama

  3. 2019-20 Highlights of Classical and Quantum Gravity

    Inflationary stochastic anomalies

    Lucas Pinol, Sébastien Renaux-Petel, Yuichiro Tada

 

論文 30

  1. Stochastic formalism for U(1) gauge fields in axion inflation

    Fujita T., Mukaida K., Tada Y.

    Journal of Cosmology and Astroparticle Physics   2022 巻 ( 12 )   2022年12月

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

    We develop the stochastic formalism for U(1) gauge fields that has the Chern-Simons coupling to a rolling pseudo-scalar field during inflation. The Langevin equations for the physical electromagnetic fields are derived and the analytic solutions are studied. Using numerical simulation we demonstrate that the electromagnetic fields averaged over the Hubble scale continuously change their direction and their amplitudes fluctuate around the analytically obtained expectation values. Though the isotropy is spontaneously broken by picking up a particular local Hubble patch, each Hubble patch is understood independent and the isotropy is conserved globally by averaging all the Hubble patches.

    DOI: 10.1088/1475-7516/2022/12/026

    Scopus

  2. Effective Inspiral Spin Distribution of Primordial Black Hole Binaries 査読有り

    Koga Yasutaka, Harada Tomohiro, Tada Yuichiro, Yokoyama Shuichiro, Yoo Chul-Moon

    ASTROPHYSICAL JOURNAL   939 巻 ( 2 )   2022年11月

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    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

    Web of Science

    Scopus

  3. Effective treatment of U(1) gauge field and charged particles in axion inflation 査読有り

    Fujita Tomohiro, Kume Jun'ya, Mukaida Kyohei, Tada Yuichiro

    JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS   2022 巻 ( 9 ) 頁: 023 - 023   2022年9月

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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 axionic inflaton with the Chern-Simons coupling may generate U(1) gauge fields and charged particles simultaneously. In order to incorporate the backreaction from the charged particles on the gauge fields, we develop a procedure to obtain an equilibrium solution for the gauge fields by treating the induced current as effective electric and magnetic conductivities. Introducing mean field approximation, and numerically solving self-consistency equations, we find that the gauge field amplitudes are drastically suppressed. Interestingly, as the production becomes more efficient, the charged particles gain a larger part of the transferred energy from the inflaton and eventually dominate it. Our formalism offers a basis to connect this class of inflationary models to a rich phenomenology such as baryogenesis and magnetogenesis.

    DOI: 10.1088/1475-7516/2022/09/023

    Web of Science

    Scopus

    その他リンク: https://iopscience.iop.org/article/10.1088/1475-7516/2022/09/023/pdf

  4. Statistics of coarse-grained cosmological fields in stochastic inflation 査読有り

    Tada Y., Vennin V.

    Journal of Cosmology and Astroparticle Physics   2022 巻 ( 02 ) 頁: 021 - 021   2022年2月

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

    We present a generic framework to compute the one-point statistics of cosmological perturbations, when coarse-grained at an arbitrary scale R, in the presence of quantum diffusion. Making use of the stochastic-δN formalism, we show how it can be related to the statistics of the amount of expansion realised until the scale R crosses out the Hubble radius. This leads us to explicit formulae for the probability density function (PDF) of the curvature perturbation, the comoving density contrast, and the compaction function. We then apply our formalism to the calculation of the mass distribution of primordial black holes produced in a single-field model containing a "quantum well"(i.e. an exactly flat region in the potential). We confirm that the PDFs feature heavy, exponential tails, with an additional cubic suppression in the case of the curvature perturbation. The large-mass end of the mass distribution is shown to be mostly driven by stochastic-contamination effects, which produce black holes more massive than those naively expected. This work bridges the final gap between the stochastic-inflation formalism and the calculation of the mass distribution of astrophysical objects such as primordial black holes, and opens up various prospects that we finally discuss.

    DOI: 10.1088/1475-7516/2022/02/021

    Scopus

    arXiv

    その他リンク: http://arxiv.org/pdf/2111.15280v2

  5. Primordial black holes in peak theory with a non-Gaussian tail 査読有り

    Kitajima N., Tada Y., Yokoyama S., Yoo C.M.

    Journal of Cosmology and Astroparticle Physics   2021 巻 ( 10 ) 頁: 053 - 053   2021年10月

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    記述言語:日本語   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

    Scopus

    arXiv

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

  6. Revisiting non-Gaussianity in non-attractor inflation models in the light of the cosmological soft theorem 査読有り

    Suyama T., Tada Y., Yamaguchi M.

    Progress of Theoretical and Experimental Physics   2021 巻 ( 7 )   2021年7月

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    記述言語:日本語   出版者・発行元:Progress of Theoretical and Experimental Physics  

    We revisit squeezed-limit non-Gaussianity in single-field non-attractor inflation models from the viewpoint of the cosmological soft theorem. In single-field attractor models, an inflaton's trajectories with different initial conditions effectively converge into a single trajectory in the phase space, and hence there is only one clock degree of freedom (DoF) in the scalar part. Its long-wavelength perturbations can be absorbed into the local coordinate renormalization and lead to the so-called consistency relation between n- and (n+1)-point functions. On the other hand, if the inflaton dynamics deviates from the attractor behavior, its long-wavelength perturbations cannot necessarily be absorbed and the consistency relation is expected not to hold any longer. In this work, we derive a formula for the squeezed bispectrum including the explicit correction to the consistency relation, as a proof of its violation in the non-attractor cases. First one must recall that non-attractor inflation needs to be followed by attractor inflation in a realistic case. Then, even if a specific non-attractor phase is effectively governed by a single DoF of phase space (represented by the exact ultra-slow-roll limit) and followed by a single-DoF attractor phase, its transition phase necessarily involves two DoF in dynamics and hence its long-wavelength perturbations cannot be absorbed into the local coordinate renormalization. Thus, it can affect local physics, even taking account of the so-called local observer effect, as shown by the fact that the bispectrum in the squeezed limit can go beyond the consistency relation. More concretely, the observed squeezed bispectrum does not vanish in general for long-wavelength perturbations exiting the horizon during a non-attractor phase.

    DOI: 10.1093/ptep/ptab063

    Scopus

  7. Induced gravitational waves as a cosmological probe of the sound speed during the QCD phase transition 査読有り

    Abe Katsuya T., Tada Yuichiro, Ueda Ikumi

    JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS   2021 巻 ( 6 ) 頁: 048 - 048   2021年6月

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

    The standard model of particle physics is known to be intriguingly successful. However, their rich phenomena represented by the phase transitions (PTs) have not been completely understood yet, including the possibility of the existence of unknown dark sectors. In this paper, we investigate the measurement of the equation of state parameter w and the sound speed cs of the PT plasma with the use of the gravitational waves (GWs) of the universe. Though the propagation of GW is insensitive to cs in itself, the sound speed value affects the dynamics of primordial density (or scalar curvature) perturbations, and the induced GW by their horizon reentry can then be an indirect probe both w and cs. We numerically reveal the concrete spectrum of the predicted induced GW with two simple examples of the scalar perturbation spectrum: The monochromatic and scale-invariant spectra. In the monochromatic case, we see that the resonant amplification and cancellation scales of the induced GW depend on the cs values at different times respectively. The scale-invariant case gives a more realistic spectrum and its specific shape will be compared with observations. In particular, the QCD phase transition corresponds with the frequency range of the pulsar timing array (PTA) observations. If the amplitude of primordial scalar power is in the range of 10-4 ? A? ? 10-2 ,the induced GW is consistent with current observational constraints and detectable in the future observation in Square Kilometer Array. Furthermore?the recent possible detection of stochastic GWs by NANOGrav 12.5 yr analysis [1] can be explained by the induced GW if A?~v 7 × 10-3.

    DOI: 10.1088/1475-7516/2021/06/048

    Web of Science

    Scopus

    arXiv

    その他リンク: https://iopscience.iop.org/article/10.1088/1475-7516/2021/06/048/pdf

  8. Minimal k -inflation in light of the conformal metric-affine geometry 査読有り

    Mikura Y., Tada Y., Yokoyama S.

    Physical Review D   103 巻 ( 10 )   2021年5月

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    記述言語:日本語   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

    Scopus

  9. A manifestly covariant theory of multifield stochastic inflation in phase space: solving the discretisation ambiguity in stochastic inflation 査読有り

    Pinol Lucas, Renaux-Petel Sebastien, Tada Yuichiro

    JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS   2021 巻 ( 4 ) 頁: 048 - 048   2021年4月

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

    Stochastic inflation is an effective theory describing the super-Hubble, coarse-grained, scalar fields driving inflation, by a set of Langevin equations. We previously highlighted the difficulty of deriving a theory of stochastic inflation that is invariant under field redefinitions, and the link with the ambiguity of discretisation schemes defining stochastic differential equations. In this paper, we solve the issue of these "inflationary stochastic anomalies"by using the Stratonovich discretisation satisfying general covariance, and identifying that the quantum nature of the fluctuating fields entails the existence of a preferred frame defining independent stochastic noises. Moreover, we derive physically equivalent Itô-Langevin equations that are manifestly covariant and well suited for numerical computations. These equations are formulated in the general context of multifield inflation with curved field space, taking into account the coupling to gravity as well as the full phase space in the Hamiltonian language, but this resolution is also relevant in simpler single-field setups. We also develop a path-integral derivation of these equations, which solves conceptual issues of the heuristic approach made at the level of the classical equations of motion, and allows in principle to compute corrections to the stochastic formalism. Using the Schwinger-Keldysh formalism, we integrate out small-scale fluctuations, derive the influence action that describes their effects on the coarse-grained fields, and show how the resulting coarse-grained effective Hamiltonian action can be interpreted to derive Langevin equations with manifestly real noises. Although the corresponding dynamics is not rigorously Markovian, we show the covariant, phase-space Fokker-Planck equation for the Probability Density Function of fields and momenta when the Markovian approximation is relevant, and we give analytical approximations for the noises' amplitudes in multifield scenarios.

    DOI: 10.1088/1475-7516/2021/04/048

    Web of Science

    Scopus

    arXiv

    その他リンク: https://iopscience.iop.org/article/10.1088/1475-7516/2021/04/048/pdf

  10. Conformal inflation in the metric-affine geometry 査読有り

    Mikura Y., Tada Y., Yokoyama S.

    EPL   132 巻 ( 3 ) 頁: 39001 - 39001   2020年11月

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    記述言語:日本語   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

    arXiv

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

  11. Local observer effect on the cosmological soft theorem 査読有り

    Suyama Teruaki, Tada Yuichiro, Yamaguchi Masahide

    PROGRESS OF THEORETICAL AND EXPERIMENTAL PHYSICS   2020 巻 ( 11 )   2020年11月

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

    Non-Gaussianities of primordial perturbations in the soft limit provide important information about the light degrees of freedom during inflation. The soft modes of the curvature perturbations, unobservable for a local observer, act to rescale the spatial coordinates. We determine how the trispectrum in the collapsed limit is shifted by the rescaling due to the soft modes. We find that the form of the inequality between the $f\mathrm{NL}$ and $\tau\mathrm{NL}$ parameters is not affected by the rescaling, demonstrating that the role of the inequality as an indicator of the light degrees of freedom remains intact. We also comment on the local observer effect on the consistency relation for ultra-slow-roll inflation.

    DOI: 10.1093/ptep/ptaa144

    Web of Science

    Scopus

    arXiv

    その他リンク: http://academic.oup.com/ptep/article-pdf/2020/11/113E01/34299933/ptaa144.pdf

  12. Escape from the swampland with a spectator field 査読有り

    Kogai Kazuhiro, Tada Yuichiro

    PHYSICAL REVIEW D   101 巻 ( 10 )   2020年5月

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

    In the context of string theory, several conjectural conditions have been proposed for low energy effective field theories not to be in swampland, the UV-incomplete class. The recent ones represented by the de Sitter and trans-Planckian censorship conjectures in particular seem to conflict with the inflation paradigm of the early universe. We first point out that scenarios where inflation is repeated several times (multiphase inflation) can be easily compatible with these conjectures. In other words, we relax the constraint on the single inflation for the large scale perturbations to only continue at least around 10 e-folds. In this context, we then investigate if a spectator field can be a source of the almost scale-invariant primordial perturbations on the large scale. As a consequence of such an isocurvature contribution, the resultant perturbations exhibit the nonvanishing non-Gaussianity in general. Also the perturbation amplitude on smaller scales can be completely different from that on the large scale due to the multiplicity of inflationary phases. These signatures will be a smoking gun of this scenario by the future observations.

    DOI: 10.1103/PhysRevD.101.103514

    Web of Science

    Scopus

    arXiv

    その他リンク: http://arxiv.org/pdf/2003.06753v2

  13. Stochastic inflation with an extremely large number of e-folds 査読有り

    Kitajima Naoya, Tada Yuichiro, Takahashi Fuminobu

    PHYSICS LETTERS B   800 巻   2020年1月

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    記述言語:日本語   掲載種別:研究論文(学術雑誌)   出版者・発行元:Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics  

    We propose a class of single-field, slow-roll inflation models in which a typical number of e-folds can be extremely large. The key point is to introduce a very shallow local minimum near the top of the potential in a hilltop inflation model. In particular, a typical number of e-folds is enhanced if classical behavior dominates around the local minimum such that the inflaton probability distribution is drifted to the local minimum as a whole. After the inflaton escapes from the local minimum due to the stochastic dynamics, the ordinary slow-roll inflation follows and it can generate the primordial density perturbation consistent with observation. Interestingly, our scenario inherits the advantages of the old and new inflation: the typical e-folds can be extremely large as in the old inflation, and slow-roll inflation naturally follows after the stochastic regime as in the new inflation. In our numerical example, the typical number of e-folds can be as large as 101010, which is large enough for various light scalars such the QCD axion to reach the Bunch-Davies distribution.

    DOI: 10.1016/j.physletb.2019.135097

    Web of Science

    Scopus

    arXiv

    その他リンク: http://arxiv.org/pdf/1908.08694v2

  14. クォーク・ハドロン相転移による背景重力波への影響

    植田 郁海, 多田 祐一郎, 阿部 克哉

    日本物理学会講演概要集   75.1 巻 ( 0 ) 頁: 543 - 543   2020年

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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.75.1.0_543

    CiNii Research

  15. Primordial black hole tower: Dark matter, earth-mass, and LIGO black holes 査読有り

    Tada Yuichiro, Yokoyama Shuichiro

    PHYSICAL REVIEW D   100 巻 ( 2 )   2019年7月

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    記述言語:日本語   掲載種別:研究論文(学術雑誌)  

    DOI: 10.1103/PhysRevD.100.023537

    Web of Science

    arXiv

    その他リンク: http://arxiv.org/pdf/1904.10298v2

  16. Inflationary stochastic anomalies 査読有り

    Pinol Lucas, Renaux-Petel Sebastien, Tada Yuichiro

    CLASSICAL AND QUANTUM GRAVITY   36 巻 ( 7 )   2019年4月

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    記述言語:日本語   掲載種別:研究論文(学術雑誌)   出版者・発行元:Classical and Quantum Gravity  

    The stochastic approach aims at describing the long-wavelength part of quantum fields during inflation by a classical stochastic theory. It is usually formulated in terms of Langevin equations, giving rise to a Fokker-Planck equation for the probability distribution function of the fields, and possibly their momenta. The link between these two descriptions is ambiguous in general, as it depends on an implicit discretisation procedure, the two prominent ones being the It- and Stratonovich prescriptions. Here we show that the requirement of general covariance under field redefinitions is verified only in the latter case, however at the expense of introducing spurious 'frame' dependences. This stochastic anomaly disappears when there is only one source of stochasticity, like in slow-roll single-field inflation, but manifests itself when taking into account the full phase space, or in the presence of multiple fields. Despite these difficulties, we use physical arguments to write down a covariant Fokker-Planck equation that describes the diffusion of light scalar fields in non-linear sigma models in the overdamped limit. We apply it to test scalar fields in de Sitter space and show that some statistical properties of a class of two-field models with derivative interactions can be reproduced by using a correspondence with a single-field model endowed with an effective potential. We also present explicit results in a simple extension of the single-field λψ 4 theory to a hyperbolic field space geometry. The difficulties we describe seem to be the stochastic counterparts of the notoriously difficult problem of maintaining general covariance in quantum theories, and the related choices of operator ordering and path-integral constructions. Our work thus opens new avenues of research at the crossroad between cosmology, statistical physics, and quantum field theory.

    DOI: 10.1088/1361-6382/ab097f

    Web of Science

    Scopus

    arXiv

    その他リンク: http://arxiv.org/pdf/1806.10126v2

  17. Does the detection of primordial gravitational waves exclude low energy inflation? 査読有り

    Fujita Tomohiro, Namba Ryo, Tada Yuichiro

    PHYSICS LETTERS B   778 巻   頁: 17 - 21   2018年3月

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    記述言語:日本語   掲載種別:研究論文(学術雑誌)  

    DOI: 10.1016/j.physletb.2017.12.014

    Web of Science

    Scopus

    arXiv

  18. O(10)M-circle dot primordial black holes and string axion dark matter 査読有り

    Inomata Keisuke, Kawasaki Masahiro, Mukaida Kyohei, Tada Yuichiro, Yanagida Tsutomu T.

    PHYSICAL REVIEW D   96 巻 ( 12 ) 頁: 123527 - 123527   2017年12月

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    記述言語:日本語   掲載種別:研究論文(学術雑誌)  

    DOI: 10.1103/PhysRevD.96.123527

    Web of Science

    Scopus

    arXiv

  19. Inflationary primordial black holes as all dark matter 査読有り

    Inomata Keisuke, Kawasaki Masahiro, Mukaida Kyohei, Tada Yuichiro, Yanagida Tsutomu T.

    PHYSICAL REVIEW D   96 巻 ( 4 ) 頁: 043504 - 043504   2017年8月

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    記述言語:日本語   掲載種別:研究論文(学術雑誌)  

    DOI: 10.1103/PhysRevD.96.043504

    Web of Science

    Scopus

    arXiv

  20. Inflationary primordial black holes for the LIGO gravitational wave events and pulsar timing array experiments 査読有り

    Inomata Keisuke, Kawasaki Masahiro, Mukaida Kyohei, Tada Yuichiro, Yanagida Tsutomu T.

    PHYSICAL REVIEW D   95 巻 ( 12 ) 頁: 123510 - 123510   2017年6月

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    記述言語:日本語   掲載種別:研究論文(学術雑誌)  

    DOI: 10.1103/PhysRevD.95.123510

    Web of Science

    Scopus

    arXiv

  21. Squeezed bispectrum in the delta N formalism: local observer effect in field space 査読有り

    Tada Yuichiro, Vennin Vincent

    JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS   1702 巻 ( 2 ) 頁: 021 - 021   2017年2月

     詳細を見る

    記述言語:日本語   掲載種別:研究論文(学術雑誌)  

    DOI: 10.1088/1475-7516/2017/02/021

    Web of Science

    Scopus

    arXiv

  22. Primordial black holes as dark matter in supergravity inflation models 査読有り

    Kawasaki Masahiro, Kusenko Alexander, Tada Yuichiro, Yanagida Tsutomu T.

    PHYSICAL REVIEW D   94 巻 ( 8 ) 頁: 083523 - 083523   2016年10月

     詳細を見る

    記述言語:日本語   掲載種別:研究論文(学術雑誌)  

    DOI: 10.1103/PhysRevD.94.083523

    Web of Science

    arXiv

  23. Revisiting constraints on small scale perturbations from big-bang nucleosynthesis 査読有り

    Inomata Keisuke, Kawasaki Masahiro, Tada Yuichiro

    PHYSICAL REVIEW D   94 巻 ( 4 ) 頁: 043527 - 043527   2016年8月

     詳細を見る

    記述言語:日本語   掲載種別:研究論文(学術雑誌)  

    DOI: 10.1103/PhysRevD.94.043527

    Web of Science

    Scopus

    arXiv

  24. Can massive primordial black holes be produced in mild waterfall hybrid inflation? 査読有り

    Kawasaki Masahiro, Tada Yuichiro

    JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS   1608 巻 ( 8 ) 頁: 041 - 041   2016年8月

     詳細を見る

    記述言語:日本語   掲載種別:研究論文(学術雑誌)  

    DOI: 10.1088/1475-7516/2016/08/041

    Web of Science

    Scopus

    arXiv

  25. 小スケールゆらぎがある中での陽子中性子比の決定

    猪又 敬介, 川崎 雅裕, 多田 祐一郎

    日本物理学会講演概要集   71 巻   頁: 328 - 328   2016年

     詳細を見る

    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  

    <p>ビッグバン元素合成が起きる時期には、ホライズン内の10^4^Mpc^-1^<k<10^5^Mpc^-1^の小スケールゆらぎはまだシルク減衰によって均されていない。我々は、まだ均されていない小スケールゆらぎがある中での陽子中性子比の決定を数値計算で評価した。特に、ホライズンに入った直後のゆらぎの振る舞いに注意して計算を行った。さらにその結果を、陽子中性子比と密接に関係する^4^Heの存在量の観測結果と比較することで小スケールゆらぎに対して制限をかけることに成功した。</p>

    DOI: 10.11316/jpsgaiyo.71.2.0_328

  26. Primordial black holes as biased tracers 査読有り

    Tada Yuichiro, Yokoyama Shuichiro

    PHYSICAL REVIEW D   91 巻 ( 12 ) 頁: 123534 - 123534   2015年6月

     詳細を見る

    記述言語:日本語   掲載種別:研究論文(学術雑誌)  

    DOI: 10.1103/PhysRevD.91.123534

    Web of Science

    Scopus

    arXiv

  27. Consistent generation of magnetic fields in axion inflation models 査読有り

    Fujita Tomohiro, Namba Ryo, Tada Yuichiro, Takeda Naoyuki, Tashiro Hiroyuki

    JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS   1505 巻 ( 5 ) 頁: 054 - 054   2015年5月

     詳細を見る

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

    There has been a growing evidence for the existence of magnetic fields in the extra-galactic regions, while the attempt to associate their origin with the inflationary epoch alone has been found extremely challenging. We therefore take into account the consistent post-inflationary evolution of the magnetic fields that are originated from vacuum fluctuations during inflation. In the model of our interest, the electromagnetic (EM) field is coupled to a pseudo-scalar inflaton φ through the characteristic term φ F, breaking the conformal invariance. This interaction dynamically breaks the parity and enables a continuous production of only one of the polarization states of the EM field through tachyonic instability. The produced magnetic fields are thus helical. We find that the dominant contribution to the observed magnetic fields in this model comes from the modes that leave the horizon near the end of inflation, further enhanced by the tachyonic instability right after the end of inflation. The EM field is subsequently amplified by parametric resonance during the period of inflaton oscillation. Once the thermal plasma is formed (reheating), the produced helical magnetic fields undergo a turbulent process called inverse cascade, which shifts their peak correlation scales from smaller to larger scales. We consistently take all these effects into account within the regime where the perturbation of φ is negligible and obtain B∼ 10-19 G, indicating the necessity of additional mechanisms to accommodate the observations.

    DOI: 10.1088/1475-7516/2015/05/054

    Web of Science

    Scopus

    arXiv

  28. Anisotropic CMB distortions from non-Gaussian isocurvature perturbations 査読有り

    Ota Atsuhisa, Sekiguchi Toyokazu, Tada Yuichiro, Yokoyama Shuichiro

    JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS   1503 巻 ( 3 ) 頁: 013 - 013   2015年3月

     詳細を見る

    記述言語:日本語   掲載種別:研究論文(学術雑誌)  

    DOI: 10.1088/1475-7516/2015/03/013

    Web of Science

    Scopus

    arXiv

  29. Non-perturbative approach for curvature perturbations in stochastic-delta N formalism 査読有り

    Fujita Tomohiro, Kawasaki Masahiro, Tada Yuichiro

    JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS   1410 巻 ( 10 ) 頁: 030 - 030   2014年10月

     詳細を見る

    記述言語:日本語   掲載種別:研究論文(学術雑誌)  

    DOI: 10.1088/1475-7516/2014/10/030

    Web of Science

    Scopus

    arXiv

  30. A new algorithm for calculating the curvature perturbations in stochastic inflation 査読有り

    Fujita Tomohiro, Kawasaki Masahiro, Tada Yuichiro, Takesako Tomohiro

    JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS   1312 巻 ( 12 ) 頁: 036 - 036   2013年12月

     詳細を見る

    記述言語:日本語   掲載種別:研究論文(学術雑誌)  

    DOI: 10.1088/1475-7516/2013/12/036

    Web of Science

    Scopus

    arXiv

▼全件表示

MISC 4

  1. Primordial Black Holes

    Albert Escrivà, Florian Kuhnel, Yuichiro Tada  

        2022年11月

     詳細を見る

    We review aspect of primordial black holes, i.e., black holes which have been
    formed in the early Universe. Special emphasis is put on their formation, their
    r\^ole as dark matter candidates and their manifold signatures, particularly
    through gravitational waves.

    arXiv

    その他リンク: http://arxiv.org/pdf/2211.05767v1

  2. Hybrid metric-Palatini Higgs inflation

    Minxi He, Yusuke Mikura, Yuichiro Tada  

        2022年9月

     詳細を見る

    We propose an extension of the Higgs inflation to the hybrid metric-Palatini
    gravity, where we introduce non-minimal couplings between Higgs and both the
    metric-type and the Palatini-type Ricci scalars. We study the inflationary
    phenomenology of our model and find that slow-roll inflation can be realized in
    the large-field regime, giving the observationally favored predictions. In
    particular, the scalar spectral index exhibits an attractor behavior to
    $n_{\mathrm{s } }\sim 0.964$, while the tensor-to-scalar ratio can take an
    arbitrary value depending on the non-minimal coupling parameters, with the
    metric-Higgs limit $r\sim10^{-3}$ being the maximum. We also investigate the
    unitarity property of our model. As the ultraviolet (UV) cutoff as a low-energy
    effective field theory (EFT) of this model is significantly lower than the
    Planck scale due to a strong curvature of field-space, we consider a possible
    candidate of UV-extended theories with an additional scalar field introduced so
    as to flatten the field-space in five-dimension. While the field-space can be
    flatten completely and this approach can lead to a weakly-coupled EFT, we gain
    an implication that Planck-scale EFT can be only realized in the limit of
    metric-Higgs inflation. We also discuss generalizations of the model up to
    mass-dimension four.

    arXiv

    その他リンク: http://arxiv.org/pdf/2209.11051v1

  3. Simulation of Primordial Black Holes with large negative non-Gaussianity

    Albert Escrivà, Yuichiro Tada, Shuichiro Yokoyama, Chul-Moon Yoo  

        2022年2月

     詳細を見る

    In this work, we have performed numerical simulations of primordial black
    hole (PBH) formation in the Friedman-Lema\^itre-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 arXiv:2109.00791, particularly for
    negative values of the non-linearity parameter $f_{\rm NL}$. Our numerical
    results show the existence of PBH formation of (the so-called) type I also in
    the case $f_{\rm NL} \lesssim -0.336$, 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 $\bar{\mathcal{C } }_{c}=2/5$ 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 $f_{\rm NL}\gtrsim -1$.

    arXiv

    その他リンク: http://arxiv.org/pdf/2202.01028v1

  4. On UV-completion of Palatini-Higgs inflation

    Yusuke Mikura, Yuichiro Tada  

        2021年10月

     詳細を見る

    We investigate the UV-completion of the Higgs inflation in the metric and the
    Palatini formalisms. It is known that the cutoff scales for the perturbative
    unitarity of these inflation models become much smaller than the Planck scale
    to be consistent with observations. Expecting that the low cutoff scale
    originates in the curvature of a field-space spanned by the Higgs fields, we
    consider embedding the curved field-space into a higher dimensional flat space
    and apply this procedure to the metric-Higgs and the Palatini-Higgs scenarios.
    The new field introduced in this way successfully flattens the field-space and
    UV-completes the Higgs inflation in the metric formalism. However, in the
    Palatini formalism, the new field cannot uplift the cutoff up to the Planck
    scale. We also discuss the unavoidable low cutoff in the Palatini formalism in
    the context of the local conformal symmetry.

    arXiv

    その他リンク: http://arxiv.org/pdf/2110.03925v1

講演・口頭発表等 9

  1. 宇宙の「インフレ」と「金融工学」 招待有り

    多田祐一郎

    名大発アカデミックフラッシュ 第2報  2021年9月3日 

     詳細を見る

    記述言語:日本語   会議種別:口頭発表(一般)  

  2. 星が先かブラックホールが先か?原始ブラックホール研究の最前線 招待有り

    多田祐一郎

    名古屋大学・名古屋市科学館 公開オンラインセミナー  2021年8月22日 

     詳細を見る

    記述言語:日本語   会議種別:公開講演,セミナー,チュートリアル,講習,講義等  

  3. 粗視化曲率ゆらぎの確率密度関数

    多田祐一郎, Vincent Vennin

    日本物理学会秋季大会  2021年9月14日 

     詳細を見る

    記述言語:日本語   会議種別:口頭発表(一般)  

  4. Primordial black holes in peak theory with a non-Gaussian tail

    Naoya Kitajima, Yuichiro Tada, Shuichiro Yokoyama, Chul-Moon Yoo

    The KEK-PH + KEK-Cosmo joint workshop on "Primordial Black Holes"  2021年10月19日 

     詳細を見る

    記述言語:日本語   会議種別:口頭発表(一般)  

  5. Primordial black holes in peak theory with a non-Gaussian tail 招待有り

    Naoya Kitajima, Yuichiro Tada, Shuichiro Yokoyama, Chul-Moon. Yoo

    2021 NRF-JSPS Workshop in particle physics, cosmology, and gravitation  2021年7月21日 

     詳細を見る

    記述言語:英語   会議種別:口頭発表(一般)  

  6. Probability density functions of coarse-grained curvature and density perturbations in stochastic inflation

    Yuichiro Tada, Vincent Vennin

    JGRG30  2021年12月9日 

     詳細を見る

    記述言語:英語   会議種別:口頭発表(一般)  

  7. Probability density functions of coarse-grained curvature and density perturbations in stochastic inflation

    Yuichiro Tada, Vincent Vennin

    COSMO'21  2021年8月2日 

     詳細を見る

    記述言語:英語   会議種別:ポスター発表  

  8. Self-introduction, or a biased view of what theoretical cosmologists are recently interested in 招待有り

    Yuichiro Tada

    E-lab seminar, Nagoya U.  2021年5月25日 

     詳細を見る

    記述言語:英語   会議種別:公開講演,セミナー,チュートリアル,講習,講義等  

  9. インフレーションの「現在」と重力波 招待有り

    多田祐一郎

    DECIGO ワークショップ  2021年12月11日 

     詳細を見る

    記述言語:日本語   会議種別:口頭発表(一般)  

▼全件表示

科研費 4

  1. 確率解析・原始ブラックホール・重力波観測から迫るインフレーション

    研究課題/研究課題番号:21K13918  2021年4月 - 2024年3月

    日本学術振興会  科学研究費助成事業 若手研究  若手研究

    多田 祐一郎

      詳細を見る

    担当区分:研究代表者 

    配分額:4680000円 ( 直接経費:3600000円 、 間接経費:1080000円 )

    本研究の目的を踏まえ具体的研究課題は次のように3つに分けられる. 1つ目はインフレーションの確率形式を理論的に整備するとともに, 数値計算プログラムを開発・公開し, さらに具体的なインフレーション理論の解析を行うことである. また本形式を応用し原始ブラックホール形成理論を探るとともに, 正確な原始ブラックホール量の計算法を確立する. そして原始ブラックホールに関連した初期重力波を通じてインフレーションに対して得られる情報を模索する.

  2. ストカスティック形式で迫る重力と量子論

    研究課題/研究課題番号:19K14707  2019年4月 - 2021年3月

    日本学術振興会  科学研究費助成事業 若手研究  若手研究

    多田 祐一郎

      詳細を見る

    担当区分:研究代表者 

    配分額:1560000円 ( 直接経費:1200000円 、 間接経費:360000円 )

    量子論と重力理論の統合は現代物理学の課題の1つであるが、両方に関係した重要な現象として重力による量子ゆらぎの古典化がある。特に宇宙初期の急激な膨張期 (インフレーション) ではこの古典化により、現在の宇宙における銀河や星などの構造の元となる密度ゆらぎを生み出したと考えられている。このように古典化したゆらぎを扱う方法としてストカスティック形式が知られており、我々はこの形式と純粋な量子論的計算を比較することで古典化の謎に迫る。同時に、ストカスティック形式では量子ゆらぎを古典ゆらぎとして簡略的に扱うことで逆に計算の幅が広がるので、これをインフレーション模型の包括的解析に応用していく。
    2020年度は計6本の論文を出版し, 特にフランスとの共同研究である "A manifestly covariant theory of multifield stochastic inflation in phase space" (arXiv: 2008.07497, JCAP accepted) ではインフレーションの確率形式を一から見直し, 共変かつ数学的に一意な定式化に成功した. また2019年に出版した, 本論文の前研究である "Inflationary stochastic anomalies" (Class. Quant. Grav. 36, no. 7, 07LT01 (2019)) は CQG の 2019--20 のハイライトに選ばれた. 一連の研究は3つの国際研究会, 1つの国内研究会, 5つのセミナーにおいて発表し, Online JGRG Workshop 2020 での発表では Outstanding Presentation Award Gold Prize を受賞した.
    研究実績に記述した通り, 本研究計画の大きな目標の1つであるインフレーションの確率形式の整備に成功し, 本成果は十二分に評価されている. これをもって本研究計画は順調に進展していると判断できる.
    インフレーションの確率形式の定式化には成功したが, これを原理的な場の量子論から厳密に正当化できたわけではない. そこでまずは本形式を様々な具体的インフレーション理論に適用しながら確率形式と量子論の整合性を事例研究的に調査し, そこから確率形式の定式化の量子論的正当化, 引いては加速膨張時空における重力の量子論への影響を議論する.

  3. インフレーション宇宙における曲率ゆらぎと原始ブラックホール形成

    研究課題/研究課題番号:18J01992  2018年4月 - 2021年3月

    日本学術振興会  科学研究費助成事業 特別研究員奨励費  特別研究員奨励費

    多田 祐一郎

      詳細を見る

    前年度に引き続きインフレーションに対するストカスティック形式を主題の1つとして研究を行った。ストカスティック形式ではインフレーション中のスカラー場のゆらぎをブラウン運動として取り入れるが、ブラウン運動の微分不可な特性からスカラー場間の共変性が崩れることに気づき、前年度所属のパリ IAP に再出張し論文にまとめ、CQG Letter に採択された[1]。その後 NCTS の北本氏により、量子論とストカスティック形式の対応に際し、タドポール図を正しく取り入れることで共変性を回復できることが、スローロール近似の下で示された[1811.01830]。現在これを近似を使わない形式に拡張すべく研究中である。
    またストカスティック形式を応用し、インフレーションによる曲率ゆらぎを非摂動的に解析する手法を数値計算ツールとして実装し学会発表した[国内 3]。現在これを公開コードとして発表する準備を行っている。
    もう1つの課題である原始ブラックホール (PBH) に関しては、同じく名古屋大学所属の横山助教とともに研究を行い、学会でも発表した[国内 4, 国外 2]。PBH の動機として我々は、暗黒物質、LIGO の重力波検出、OGLE による自由惑星の重力レンズ現象の発見の3つに注目し、インフレーションを複数段階に分けることでこれらを同時に説明する PBH 質量スペクトルを実現できることを示した。こうした複数段階インフレーションは、最近発表された string swampland conjecture [1810.05506] からも支持されることを指摘している。これらの結果を論文として発表する準備の途中である。
    最後に同研究室学生の阿部氏とは、振動するスカラー場の重力崩壊現象について研究を行っている。

  4. 小スケール曲率ゆらぎの観測とインフレーション

    研究課題/研究課題番号:15J10829  2015年4月 - 2017年3月

    日本学術振興会  科学研究費助成事業 特別研究員奨励費  特別研究員奨励費

    多田 祐一郎

      詳細を見る

    昨年度は5本の論文 (arXiv:1605.04646, 1606.07631, 1609.08876, 1611.06130, 1701.02544) を提出した。1つ目の論文では小スケールにもし大きな曲率ゆらぎが生じていた場合、それがビッグバン元素合成に与える影響について再考察し、既存の結果が定性的レベルで修正されることを示した。また3つ目の論文では、曲率ゆらぎのスクィーズド極限バイスペクトルに関し、近年指摘されているゲージ依存効果についての新たな理解を示し、簡単な計算アルゴリズムを提唱した。これは今後、実際に何らかの観測 (宇宙背景放射や銀河バイアス等) によってバイスペクトルを測定し、それを宇宙初期の物理と対応させるときに非常に重要になってくる。残りの論文では原始ブラックホールについて議論している。昨年 LIGO グループが初の重力波直接検出を発表し話題になったが、この重力波は重いブラックホール連星の合体から来ており、こうしたブラックホールが原始ブラックホールである可能性も注目されてきている。また伴って、原始ブラックホールが暗黒物質である可能性も再注目されてきた。そこで我々は実際に具体的なインフレーション模型を構築し、原始ブラックホールが LIGO の重力波イベントや暗黒物質を説明しうるか、また他に検出方法があるかどうかなどを検証した。
    これら研究成果に関し、国際会議で2度, 国内会議で1度口頭発表を行った. また国内外合わせて4つの研究機関でセミナー発表を行った.

 

担当経験のある科目 (本学以外) 1

  1. 力学1, 2

    2019年4月 - 現在 大同大学)