We study relativistic effects, arising from the light propagation in an
inhomogeneous universe. We particularly investigate the effects imprinted in a
cross-correlation function between galaxy positions and intrinsic galaxy shapes
(GI correlation). Considering the Doppler and gravitational redshift effects as
major relativistic effects, we present an analytical model of the GI
correlation function, from which we find that the relativistic effects induce
non-vanishing odd multipole anisotropies. Focusing particularly on the dipole
anisotropy, we show that the Doppler effect dominates at large scales, while
the gravitational redshift effect originated from the halo potential dominates
at the scales below $10$-$30\, {\rm Mpc}/h$, with the amplitude of the dipole
GI correlation being positive over all the scales. Also, we newly derive the
covariance matrix for the modelled GI dipole. Taking into account the full
covariance, we estimate the signal-to-noise ratio and show that the GI dipole
induced by the relativistic effects is detectable in future large-volume galaxy
surveys. We discuss how the measurement of dipole GI correlation could be
helpful to detect relativistic effects in combination with the conventional
galaxy-galaxy cross correlation.

DOI： 10.1093/mnras/stac3462

arXiv

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その他リンク： http://arxiv.org/pdf/2207.03454v2

The local position invariance (LPI) is one of the three major pillars of
Einstein equivalence principle, ensuring the space-time independence on the
outcomes of local experiments. The LPI has been tested by measuring the
gravitational redshift effect in various depths of gravitational potentials. We
propose a new cosmological test of the LPI by observing the asymmetry in the
cross-correlation function between different types of galaxies, which
predominantly arises from the gravitational redshift effect induced by the
gravitational potential of halos at which the galaxies reside. We show that the
ongoing and upcoming galaxy surveys can give a fruitful constraint on the
LPI-violating parameter, $\alpha$, at distant universes (redshift
$z\sim0.1-1.8$) over the cosmological scales (separation $s\sim5-10\, {\rm
Mpc}/h$) that have not yet been explored, finding that the expected upper limit
on $\alpha$ can reach $0.03$.

DOI： 10.1093/mnras/stad2191

arXiv

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その他リンク： http://arxiv.org/pdf/2112.07727v2

We explore the structure around shell-crossing time of cold dark matter
protohaloes seeded by two or three crossed sine waves of various relative
initial amplitudes, by comparing Lagrangian perturbation theory (LPT) up to
10th order to high-resolution cosmological simulations performed with the
public Vlasov code ColDICE. Accurate analyses of the density, the velocity, and
related quantities such as the vorticity are performed by exploiting the fact
that ColDICE can follow locally the phase-space sheet at the quadratic level.
To test LPT predictions beyond shell-crossing, we employ a ballistic
approximation, which assumes that the velocity field is frozen just after
shell-crossing. In the generic case, where the amplitudes of the sine waves are
all different, high-order LPT predictions match very well the exact solution,
even beyond collapse. As expected, convergence slows down when going from
quasi-1D dynamics where one wave dominates over the two others, to the
axial-symmetric configuration, where all the amplitudes of the waves are equal.
It is also noticed that LPT convergence is slower when considering velocity
related quantities. Additionally, the structure of the system at and beyond
collapse given by LPT and the simulations agrees very well with singularity
theory predictions, in particular with respect to the caustic and vorticity
patterns that develop beyond collapse. Again, this does not apply to
axial-symmetric configurations, that are still correct from the qualitative
point of view, but where multiple foldings of the phase-space sheet produce
very high density contrasts, hence a strong backreaction of the gravitational
force.

DOI： 10.1051/0004-6361/202142756

arXiv

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その他リンク： http://arxiv.org/pdf/2111.08836v2

It has been recently recognized that the observational relativistic effects,
mainly arising from the light propagation in an inhomogeneous universe, induce
the dipole asymmetry in the cross-correlation function of galaxies. In
particular, the dipole asymmetry at small scales is shown to be dominated by
the gravitational redshift effects. In this paper, we exploit a simple
analytical description for the dipole asymmetry in the cross-correlation
function valid at quasi-linear regime. In contrast to the previous model, a new
prescription involves only one dimensional integrals, providing a faster way to
reproduce the results obtained by Saga et al. (2020). Using the analytical
model, we discuss the detectability of the dipole signal induced by the
gravitational redshift effect from upcoming galaxy surveys. The gravitational
redshift effect at small scales enhances the signal-to-noise ratio (S/N) of the
dipole, and in most of the cases considered, the S/N is found to reach a
maximum at $z\approx0.5$. We show that current and future surveys such as DESI
and SKA provide an idealistic data set, giving a large S/N of $10\sim 20$. Two
potential systematics arising from off-centered galaxies are also discussed
(transverse Doppler effect and diminution of the gravitational redshift
effect), and their impacts are found to be mitigated by a partial cancellation
between two competitive effects. Thus, the detection of the dipole signal at
small scales is directly linked to the gravitational redshift effect, and
should provide an alternative route to test gravity.

DOI： 10.1093/mnras/stac186

arXiv

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その他リンク： http://arxiv.org/pdf/2109.06012v2

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

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arXiv

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その他リンク： http://arxiv.org/pdf/2002.01286v2

The observed galaxy distribution via galaxy redshift surveys appears
distorted due to redshift-space distortions (RSD). While one dominant
contribution to RSD comes from the Doppler effect induced by the peculiar
velocity of galaxies, the relativistic effects, including the gravitational
redshift effect, are recently recognized to give small but important
contributions. Such contributions lead to an asymmetric galaxy clustering along
the line of sight, and produce non-vanishing odd multipoles when
cross-correlating between different biased objects. However, non-zero odd
multipoles are also generated by the Doppler effect beyond the distant-observer
approximation, known as the wide-angle effect, and at quasi-linear scales, the
interplay between wide-angle and relativistic effects becomes significant. In
this paper, based on the formalism developed by Taruya et al., we present a
quasi-linear model of the cross-correlation function taking a proper account of
both the wide-angle and gravitational redshift effects, as one of the major
relativistic effects. Our quasi-linear predictions of the dipole agree well
with simulations even at the scales below $20\,h^{-1}\,$Mpc, where
non-perturbative contributions from the halo potential play an important role,
flipping the sign of the dipole amplitude. When increasing the bias difference
and redshift, the scale where the sign flip happens is shifted to a larger
scale. We derive a simple approximate formula to quantitatively account for the
behaviors of the sign flip.

DOI： 10.1093/mnras/staa2232

arXiv

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その他リンク： http://arxiv.org/pdf/2004.03772v2

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 bNL, 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 (bNL(Bλ/nG)2) ≲− 36.5nB − 94.0 with Bλ and nB 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

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arXiv

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その他リンク： http://arxiv.org/pdf/1904.09121v2

Redshift-space distortions (RSD) in galaxy redshift surveys generally break
both the isotropy and homogeneity of galaxy distribution. While the former
aspect is particularly highlighted as a probe of growth of structure induced by
gravity, the latter aspect, often quoted as wide-angle RSD but ignored in most
of the cases, will become important and critical to account for as increasing
the statistical precision in next-generation surveys. However, the impact of
wide-angle RSD has been mostly studied using linear perturbation theory. In
this paper, employing the Zel'dovich approximation, i.e., first-order
Lagrangian perturbation theory for gravitational evolution of matter
fluctuations, we present a quasi-linear treatment of wide-angle RSD, and
compute the cross-correlation function. The present formalism consistently
reproduces linear theory results, and can be easily extended to incorporate
relativistic corrections (e.g., gravitational redshift).

DOI： 10.1093/mnras/stz3272

arXiv

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その他リンク： http://arxiv.org/pdf/1908.03854v2

We present robust constraints on the stochastic gravitational waves (GWs) at
Mpc scales from the cosmic microwave background (CMB) data. CMB constraints on
GWs are usually characterized as the tensor-to-scalar ratio, assuming
specifically a power-law form of the primordial spectrum, and are obtained from
the angular spectra of CMB. Here, we relax the assumption of the power-law
form, and consider to what extent one can constrain a monochromatic GW at
shorter wavelengths. Previously, such a constraint has been derived at the
wavelengths larger than the resolution scale of the CMB measurements, typically
above $100$Mpc (below $10^{-16}$Hz in frequency). However, GWs whose wavelength
is much shorter than $100$Mpc can imprint a small but non-negligible signal on
CMB anisotropies at observed angular scales, $\ell<1000$. Here, using the CMB
temperature, polarization, and lensing data set, we obtain the best constraints
to date at $10^{-16}-10^{-14}$Hz of the GWs produced before the time of
decoupling, which are tighter than those derived from the astrometric
measurements and upper bounds on extra radiations. In the future, the
constraints on GWs at Mpc scales will be further improved by several orders of
magnitude with the precision $B$-mode measurement on large scales, $\ell<100$.

DOI： 10.1103/PhysRevD.100.021303

arXiv

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その他リンク： http://arxiv.org/pdf/1904.02115v2

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

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arXiv

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その他リンク： http://arxiv.org/pdf/1807.00561v2

We consider the growth of primordial dark matter halos seeded by three
crossed initial sine waves of various amplitudes. Using a Lagrangian treatment
of cosmological gravitational dynamics, we examine the convergence properties
of a high-order perturbative expansion in the vicinity of shell-crossing, by
comparing the analytical results with state-of-the-art high resolution
Vlasov-Poisson simulations. Based on a quantitative exploration of parameter
space, we study explicitly for the first time the convergence speed of the
perturbative series, and find, in agreement with intuition, that it slows down
when going from quasi one-dimensional initial conditions (one sine wave
dominating) to quasi triaxial symmetry (three sine waves with same amplitude).
In most cases, the system structure at collapse time is, as expected, very
similar to what is obtained with simple one-dimensional dynamics, except in the
quasi-triaxial regime, where the phase-space sheet presents a velocity spike.
In all cases, the perturbative series exhibits a generic convergence behavior
as fast as an exponential of a power-law of the order of the expansion,
allowing one to numerically extrapolate it to infinite order. The results of
such an extrapolation agree remarkably well with the simulations, even at
shell-crossing.

DOI： 10.1103/PhysRevLett.121.241302

arXiv

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その他リンク： http://arxiv.org/pdf/1805.08787v2

The apparent distribution of large-scale structures in the universe is
sensitive to the velocity/potential of the sources as well as the potential
along the line-of-sight through the mapping from real space to redshift space
(redshift-space distortions, RSD). Since odd multipoles of the halo
cross-correlation function vanish when considering standard Doppler RSD, the
dipole is a sensitive probe of relativistic and wide-angle effects. We build a
catalogue of ten million haloes (Milky-Way size to galaxy-cluster size) from
the full-sky light-cone of a new "RayGalGroupSims" N-body simulation which
covers a volume of ($2.625~h^{-1}$Gpc)$^3$ with $4096^3$ particles. Using
ray-tracing techniques, we find the null geodesics connecting all the sources
to the observer. We then self-consistently derive all the relativistic
contributions (in the weak-field approximation) to RSD: Doppler, transverse
Doppler, gravitational, lensing and integrated Sachs-Wolfe. It allows us, for
the first time, to disentangle all contributions to the dipole from linear to
non-linear scales. At large scale, we recover the linear predictions dominated
by a contribution from the divergence of neighbouring line-of-sights. While the
linear theory remains a reasonable approximation of the velocity contribution
to the dipole at non-linear scales it fails to reproduce the potential
contribution below $30-60~h^{-1}$Mpc (depending on the halo mass). At scales
smaller than $\sim 10~h^{-1}$Mpc, the dipole is dominated by the asymmetry
caused by the gravitational redshift. The transition between the two regimes is
mass dependent as well. We also identify a new non-trivial contribution from
the non-linear coupling between potential and velocity terms.

DOI： 10.1093/mnras/sty3206

arXiv

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その他リンク： http://arxiv.org/pdf/1803.04294v2

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, B0 ≲ 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, B0 ≲ 10-17, 10-23, and 10-29 nG at 1 comoving Mpc for nB = 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

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arXiv

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その他リンク： http://arxiv.org/pdf/1708.08225v2

出版者・発行元：Physical Review D  

Cosmological defects result from cosmological phase transitions in the early Universe and the dynamics reflects their symmetry-breaking mechanisms. These cosmological defects may be probed through weak lensing effects because they interact with ordinary matters only through the gravitational force. In this paper, we investigate global textures by using weak lensing curl and B modes. Nontopological textures are modeled by the nonlinear sigma model (NLSM) and induce not only the scalar perturbation but also vector and tensor perturbations in the primordial plasma due to the nonlinearity in the anisotropic stress of scalar fields. We show angular power spectra of curl and B modes from both vector and tensor modes based on the NLSM. Furthermore, we give the analytic estimations for curl and B-mode power spectra. The amplitude of weak lensing signals depends on a combined parameter ϵv2=N-1(v/mpl)4 where N and v are the number of the scalar fields and the vacuum expectation value, respectively. We discuss the detectability of the curl and B modes with several observation specifications. In the case of the CMB lensing observation without including the instrumental noise, we can reach ϵv≈2.7×10-6. This constraint is about 10 times stronger than the current one determined from the Planck. For the cosmic shear observation, we find that the signal-to-noise ratio depends on the mean redshift and the observing number of galaxies as zm0.7 and Ng0.2, respectively. In the study of textures using cosmic shear observations, the mean redshift would be one of the key design parameters.

DOI： 10.1103/PhysRevD.95.123524

Web of Science

Scopus

arXiv

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その他リンク： http://arxiv.org/pdf/1612.04006v2

出版者・発行元：Physical Review D  

The second-order vector mode is inevitably induced from the coupling of first-order scalar modes in cosmological perturbation theory and might hinder a possible detection of primordial gravitational waves from inflation through 21 cm lensing observations. Here, we investigate the weak lensing signal in 21 cm photons emitted by neutral hydrogen atoms in the dark ages induced by the second-order vector mode by decomposing the deflection angle of the 21 cm lensing signal into the gradient and curl modes. The curl mode is a good tracer of the cosmological vector and tensor modes since the scalar mode does not induce the curl one. By comparing angular power spectra of the 21 cm lensing curl mode induced by the second-order vector mode and primordial gravitational waves whose amplitude is parametrized by the tensor-to-scalar ratio r, we find that the 21 cm curl mode from the second-order vector mode dominates over that from primordial gravitational waves on almost all scales if râ‰10-5. If we use the multipoles of the power spectrum up to â.,"max=105 and 106 in reconstructing the curl mode from 21 cm temperature maps, the signal-to-noise ratios of the 21 cm curl mode from the second-order vector mode achieve S/N≈0.46 and 73, respectively. Observation of 21 cm radiation is, in principle, a powerful tool to explore not only the tensor mode but also the cosmological vector mode.

DOI： 10.1103/PhysRevD.94.063523

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arXiv

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その他リンク： http://arxiv.org/pdf/1607.03973v2

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

The vector mode of cosmological perturbation theory imprints characteristic signals on the weak lensing signals such as curl and B modes which are never imprinted by the scalar mode. However, the vector mode is neglected in the standard first-order cosmological perturbation theory since it only has a decaying mode. This situation changes if the cosmological perturbation theory is expanded up to second order. The second-order vector and tensor modes are inevitably induced by the product of the first-order scalar modes. We study the effect of the second-order vector mode on the weak lensing curl and B modes. We find that the curl mode induced by the second-order vector mode is comparable to that induced by the primordial gravitational waves with the tensor-to-scalar ratio r=0.1 at ≈200. In this case, the curl mode induced by the second-order vector mode dominates at >200. Furthermore, the B-mode cosmic shear induced by the second-order vector mode dominates on almost all scales. However, we find that the observational signatures of the second-order vector and tensor modes cannot exceed the expected noise of ongoing and upcoming weak lensing measurements. We conclude that the curl and B modes induced by the second-order vector and tensor modes are unlikely to be detected in future experiments.

DOI： 10.1103/PhysRevD.92.063533

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arXiv

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その他リンク： http://arxiv.org/pdf/1505.02774v2

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

If vector type perturbations are present in the primordial plasma before recombination, the generation of magnetic fields is known to be inevitable through the Harrison mechanism. In the context of the standard cosmological perturbation theory, nonlinear couplings of first-order scalar perturbations create second-order vector perturbations, which generate magnetic fields. Here we reinvestigate the generation of magnetic fields at second-order in cosmological perturbations on the basis of our previous study, and extend it by newly taking into account the time evolution of purely second-order vector perturbations with a newly developed second-order Boltzmann code. We confirm that the amplitude of magnetic fields from the product-terms of the first-order scalar modes is consistent with the result in our previous study. However, we find, both numerically and analytically, that the magnetic fields from the purely second-order vector perturbations partially cancel out the magnetic fields from one of the product-terms of the first-order scalar modes, in the tight coupling regime in the radiation dominated era. Therefore, the amplitude of the magnetic fields on small scales, k10hMpc-1, is smaller than the previous estimates. The amplitude of the generated magnetic fields at cosmological recombination is about Brec=5.0×10-24Gauss on k=5.0×10-1hMpc-1. Finally, we discuss the reason for the discrepancies that exist in estimates of the amplitude of magnetic fields among other authors.

DOI： 10.1103/PhysRevD.91.123510

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arXiv

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その他リンク： http://arxiv.org/pdf/1504.03790v2

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

Gravitational waves (GWs) are inevitably induced at second order in cosmological perturbations through nonlinear couplings with first-order scalar perturbations, the existence of which is well established by recent cosmological observations. So far, the evolution and the spectrum of the secondary induced GWs have been derived by taking into account the sources of GWs only from the product of first-order scalar perturbations. Here we newly investigate the effects of purely second-order anisotropic stresses of photons and neutrinos on the evolution of GWs, which have been omitted in the literature. We present a full treatment of the Einstein-Boltzmann system to calculate the spectrum of GWs with anisotropic stress based on the formalism of the cosmological perturbation theory. We find that photon anisotropic stress amplifies the amplitude of GWs by about 150%, whereas neutrino anisotropic stress suppresses that of GWs by about 30% on small scales k1.0hMpc-1 compared to the case without anisotropic stress. The second-order anisotropic stress does not affect GWs with wave numbers k1.0hMpc-1. The result is in marked contrast with the case at linear order, where the effect of anisotropic stress is damping in the amplitude of GWs.

DOI： 10.1103/PhysRevD.91.024030

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arXiv

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その他リンク： http://arxiv.org/pdf/1412.1081v2

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

The B-mode polarization spectrum of the Cosmic Microwave Background (CMB) may be the smoking gun of not only the primordial tensor mode but also of the primordial vector mode. If there exist nonzero vector-mode metric perturbations in the early Universe, they are known to be supported by anisotropic stress fluctuations of free-streaming particles such as neutrinos, and to create characteristic signatures on both the CMB temperature, E-mode, and B-mode polarization anisotropies. We place constraints on the properties of the primordial vector mode characterized by the vector-to-scalar ratio r v and the spectral index n v of the vector-shear power spectrum, from the Planck and BICEP2 B-mode data. We find that, for scale-invariant initial spectra, the ΛCDM model including the vector mode fits the data better than the model including the tensor mode. The difference in χ2 between the vector and tensor models is Δχ2 = 3.294, because, on large scales the vector mode generates smaller temperature fluctuations than the tensor mode, which is preferred for the data. In contrast, the tensor mode can fit the data set equally well if we allow a significantly blue-tilted spectrum. We find that the best-fitting tensor mode has a large blue tilt and leads to an indistinct reionization bump on larger angular scales. The slightly red-tilted vector mode supported by the current data set can also create (10-22)-Gauss magnetic fields at cosmological recombination. Our constraints should motivate research that considers models of the early Universe that involve the vector mode.

DOI： 10.1088/1475-7516/2014/10/004

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arXiv

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その他リンク： http://arxiv.org/pdf/1405.4810v2

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

We investigate parity-violating signatures of temperature and polarization bispectra of the cosmic microwave background (CMB) in an inflationary model where a rolling pseudoscalar produces large equilateral tensor non-Gaussianity. By a concrete computation based on full-sky formalism, it is shown that resultant CMB bispectra have nonzero signals in both parity-even (ℓ1+ℓ2+ℓ3 = even) and parity-odd (ℓ1+ℓ2+ℓ3 = odd) spaces, and are almost uncorrelated with usual scalar-mode equilateral bispectra. These characteristic signatures and polarization information help to detect such tensor non-Gaussianity. Use of both temperature and E-mode bispectra potentially improves of 400% the detectability with respect to an analysis with temperature bispectrum alone. Considering B-mode bispectrum, the signal-to-noise ratio may be able to increase by 3 orders of magnitude. We present the 1σ uncertainties of a parameter depending on a coupling constant and a rolling condition for the pseudoscalar expected in the Planck and the proposed PRISM experiments. © 2013 IOP Publishing Ltd and Sissa Medialab srl.

DOI： 10.1088/1475-7516/2013/11/051

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arXiv

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その他リンク： http://arxiv.org/pdf/1308.6769v2

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

Recently the lower bounds of the intergalactic magnetic fields 10 -16∼10-20 G are set by gamma-ray observations while it is unlikely to generate such large scale magnetic fields through astrophysical processes. It is known that large scale magnetic fields could be generated if there exist cosmological vector-mode perturbations in the primordial plasma. The vector mode, however, has only a decaying solution in general relativity if the plasma consists of perfect fluids. In order to investigate a possible mechanism of magnetogenesis in the primordial plasma, here we consider cosmological perturbations in the Einstein-aether gravity model, in which the aether field can act as a new source of vector metric perturbations. The vector metric perturbations induce the velocity difference between baryons and photons which then generate magnetic fields. This velocity difference arises from effects at the second order in the tight-coupling approximation. We estimate the angular power spectra of temperature and B-mode polarization of the cosmic microwave background anisotropies in this model and put a rough constraint on the aether field parameters from latest observations. We then estimate the power spectrum of associated magnetic fields around the recombination epoch within this limit. It is found that the spectrum has a characteristic peak at k=0.1h Mpc -1, and at that scale the amplitude can be as large as B∼10 -22 G where the upper bound comes from cosmic microwave background temperature anisotropies. The magnetic fields with this amplitude can be seeds of large scale magnetic fields observed today if the sufficient dynamo mechanism takes place. Analytic interpretation for the power spectra is also given. © 2013 American Physical Society.

DOI： 10.1103/PhysRevD.87.104025

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その他リンク： http://arxiv.org/pdf/1302.4189v2

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

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arXiv

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その他リンク： http://arxiv.org/pdf/1209.3384v2