arXiv subjects

Hiroyuki Tashiro

Publications and source records attributed to Hiroyuki Tashiro.

At least 37 records · Page 2Linked to original sources

arXiv2021

Small-scale CMB anisotropies induced by the primordial magnetic fields

The primordial magnetic fields (PMFs) produced in the early universe are expected to be the origin of the large-scale cosmic magnetic fields. The PMFs are considered to leave a footprint on the cosmic microwave background (CMB) anisotropies due to both the electromagnetic force and gravitational interaction. In this paper, we investigate how the PMFs affect the CMB anisotropies on smaller scales than the mean-free-path of the CMB photons. We solve the baryon Euler equation with Lorentz force due to the PMFs, and we show that the vector-type perturbations from the PMFs induce the CMB anisotropies below the Silk scale as $\ell>3000$. Based on our calculations, we put a constraint on the PMFs from the combined CMB temperature anisotropies obtained by Planck and South Pole Telescope (SPT). We have found that the highly-resolved temperature anisotropies of the SPT 2017 bandpowers at $\ell \lesssim 8000$ favor the PMF model with a small scale-dependence. As a result, the Planck and SPT's joint-analysis puts a constraint on the PMF spectral index as $n_B<-1.14$ at 95% confidence level (C.L.), and this is more stringent compared with the Planck-only constraint $n_B<-0.28$. We show that the PMF strength normalized on the co-moving 1 Mpc scale is also tightly constrained as $B_{1\mathrm{Mpc}}<1.5$ nG with Planck and SPT at 95% C.L., while $B_{1\mathrm{Mpc}}<3.2$ nG only with the Planck data at 95% C.L. We also discuss the effects on the cosmological parameter estimate when including the SPT data and CMB anisotropies induced by the PMFs.

astro-ph.CO↗

arXiv2021

Constraining the luminosity function of active galactic nuclei through the reionization observations in the SKA era

Ultraviolet (UV) and X-ray photons from active galactic nuclei (AGNs) can ionize hydrogen in the intergalactic medium (IGM). We solve radiative transfer around AGNs in high redshift to evaluate the 21-cm line emission from the neutral hydrogen in the IGM and obtain the radial profile of the brightness temperature in the epoch of reionization. The ionization profile extends over 10 [Mpc] comoving distance which can be observed in the order of 10 [arcmin]. From estimation of the radio galaxy number counts with high sensitivity observation through the Square Kilometre Array (SKA), we investigate the capability of parameter constrains for AGN luminosity function with Fisher analysis for three evolution model through cosmic time. We find that the errors for each parameter are restricted to a few percent when AGNs are sufficiently bright at high redshifts. We also investigate the possibility of further parameter constraints with future observation beyond the era of SKA.

astro-ph.GA↗

arXiv2020

The 21-cm signals from ultracompact minihalos as a probe of primordial small-scale fluctuations

Ultracompact minihalos~(UCMHs) can form after the epoch of matter-radiation equality, if the density fluctuations of dark matter have significantly large amplitude on small scales. The constraint on the UCMH abundance allows us to access such small-scale fluctuations. In this paper, we present that, through the measurement of 21-cm fluctuations before the epoch of reionization~ we can obtain a constraint on the UCMH abundance. We calculate the 21-cm signal from UCMHs and show that UCMHs provide the enhancement of the 21-cm fluctuations. We also investigate the constraint on the UCMH abundance and small-scale curvature perturbations. Our results indicate that the upcoming 21-cm observation, the Square Kilometre Array (SKA), provides the constraint on amplitude of primordial curvature power spectrum, ${\cal A}_ζ \lesssim 10^{-6}$ on $100~{\rm Mpc}^{-1} \lesssim k \lesssim 1000~{\rm Mpc}^{-1}$. Although it is not stronger than the one from the non-detection of gamma rays induced by dark matter annihilation in UCMHs, the constraint by the SKA will be important because this constraint is independent of the dark matter particle model.

astro-ph.CO↗

arXiv2020

Limits on primordial magnetic fields from primordial black hole abundance

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 $10^{2}\;{\rm Mpc}^{-1} \leq k\leq 10^{18}\;{\rm Mpc}^{-1}$ where the typical cosmological observations never reach.

astro-ph.CO↗

arXiv2020

The Alcock Paczynski test with 21cm intensity field

Feasibility of the Alcock Paczynski (AP) test by stacking voids in the 21cm line intensity field is presented. We analyze the Illstris-TNG simulation to obtain the 21cm signal map. We then randomly distribute particles depending on the 21cm intensity field to find voids by using publicly available code, VIDE. As in the galaxy clustering, the shape of the stacked void in the 21cm field is squashed along the line of sight due to the peculiar velocities in redshift-space, although it becomes spherical in real-space. The redshift-space distortion for the stacked void weakly depends on redshift and we show that the dependency can be well described by the linear prediction, with the amplitude of the offset being free parameters. We find that the AP test using the stacked voids in a 21cm intensity map is feasible and the parameter estimation on $Ω_{\rm m}$ and $w$ is unbiased.

astro-ph.CO↗

arXiv2019

Secondary CMB temperature anisotropies from magnetic reheating

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 {\it inhomogeneous magnetic reheating}. We find that it can bring us information about non-linear coupling between PMFs and primordial curvature perturbations parametrized by $b_{\rm NL}$, 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 $\log (b_{\rm NL} (B_λ/{\rm nG})^2) \lesssim {-36.5n_{B} - 94.0}$ with $B_λ$ and $n_{\rm B}$ being a magnetic field amplitude smoothed over $λ=1\; {\rm Mpc}$ 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., $1\; {\rm Mpc}^{-1} \lesssim k\lesssim 10^{15}\; {\rm Mpc}^{-1}$.

astro-ph.CO↗

arXiv2019

Cross-correlation between 21-cm radiation and CMB B modes from the cosmic birefringence in the presence of a light scalar field

We study the cross-correlation between the 21cm and CMB B mode fluctuations which are induced by the cosmic birefringence when the non-constant scalar field couples to the electromagnetic field strength. Such multi-wavelength signals can potentially probe the reionization history of the Universe and also explore the nature of fundamental physics such as the parity violation and the scalar field dynamics in the early Universe. We illustrate the feasibility to detect such 21cm-B mode cross-correlations through commonly discussed scalar field models, the quintessence-like scalar field which is responsible for the current dark energy and the axion-like scalar field which is responsible for the current dark matter density.

astro-ph.CO↗

arXiv2019

Resonant magnetogenesis from axions

We investigate the generation of seed magnetic field through the Chern-Simons coupling between the U(1) gauge field and an axion field that commences to oscillate at various epoch, depending on the mass scale. We address axions which begin oscillation during inflation, reheating, and also the radiation dominated era after the thermalization of the Universe. We study the resonant generation mechanisms and highlight that a small oscillation time scale with respect to that of the cosmic expansion can lead to an efficient generation of (hyper) magnetic field via resonant generation, even for ${\cal O}(1)$ coupling. In addition, we demonstrate that the generated field can be helical due to the tachyonic amplification phase prior to the onset of oscillation. Furthermore, it is shown that the parametric resonance during reheating can generate a circularly polarized (hyper) magnetic field in a void region with the present amplitude $B_0 =3\times 10^{-15}$Gauss and the coherent length $λ_0 = 0.3$pc without being plagued by the backreaction issue.

astro-ph.CO↗

arXiv2019

Insight into primordial magnetic fields from 21-cm line observation with EDGES experiment

The recent observation of the 21-cm global absorption signal by EDGES suggests that the intergalactic medium (IGM) gas has been cooler than the cosmic microwave background during $15 \lesssim z \lesssim 20$. This result can provide a strong constraint on heating sources for the IGM gas at these redshifts. In this paper we study the constraint on the primordial magnetic fields (PMFs) by the EDGES result. The PMFs can heat the IGM gas through their energy dissipation due to the magnetohydrodynamic effects. By numerically solving the thermal evolution of the IGM gas with the PMFs, we find that the EDGES result gives a stringent limit on the PMFs as $B_{1\mathrm{Mpc}} \lesssim 10^{-10}$ G.

astro-ph.CO↗

arXiv2019

Sunyaev-Zel'dovich anisotropy due to Primordial black holes

We investigate the Sunyaev-Zel'dovich (SZ) effect caused by primordial black holes (PBHs) on the cosmic microwave background (CMB) temperature fluctuations. The gas accreting on a PBH heats up by the release of the gravitational energy. As a result, the heated gas in the vicinity of the PBH emits the UV and X-ray photons. These photons can ionize and heat the intergalactic medium (IGM) around the PBH. Assuming the simple model of these emitting photons, we compute the profiles of the IGM ionization fraction and temperature around a PBH. Using these profiles, we evaluate the Compton $y$-parameter created by the IGM gas around a PBH. Finally, we estimate the CMB temperature angular power spectrum due to the PBH SZ effect in our model. We show that the SZ temperature anisotropy due to the PBHs has the flat angular power spectrum on small scale, $l\leq2000$ and could dominate the primordial temperature spectrum on smaller scales than the Silk scale. This flat spectrum extends to the scale of the ionized region by the PBH emission. We also discuss the impact of the small-scale CMB measurement on the PBH abundance based on our results.

astro-ph.CO↗

arXiv2019

Measurement of redshift dependent cross correlation of HSC clusters and Fermi $γ$ rays

The cross-correlation study of the unresolved $γ$-ray background (UGRB) with galaxy clusters has a potential to reveal the nature of the UGRB. In this paper, we perform a cross-correlation analysis between $γ$-ray data by the Fermi Large Area Telescope (Fermi-LAT) and a galaxy cluster catalogue from the Subaru Hyper Suprime-Cam (HSC) survey. The Subaru HSC cluster catalogue provides a wide and homogeneous large-scale structure distribution out to the high redshift at $z=1.1$, which has not been accessible in previous cross-correlation studies. We conduct the cross-correlation analysis not only for clusters in the all redshift range ($0.1 < z < 1.1$) of the survey, but also for subsamples of clusters divided into redshift bins, the low redshift bin ($0.1 < z < 0.6$) and the high redshift bin ($0.6 < z < 1.1$), to utilize the wide redshift coverage of the cluster catalogue. We find the evidence of the cross-correlation signals with the significance of 2.0-2.3$σ$ for all redshift and low-redshift cluster samples. On the other hand, for high-redshift clusters, we find the signal with weaker significance level (1.6-1.9$σ$). We also compare the observed cross-correlation functions with predictions of a theoretical model in which the UGRB originates from $γ$-ray emitters such as blazars, star-forming galaxies and radio galaxies. We find that the detected signal is consistent with the model prediction.

astro-ph.CO↗

arXiv2018

Thermal Sunyaev-Zel'dovich effect in the intergalactic medium with primordial magnetic fields

The presence of ubiquitous magnetic fields in the universe is suggested from observations of radiation and cosmic ray from galaxies or the intergalactic medium (IGM). One possible origin of cosmic magnetic fields is the magnetogenesis in the primordial universe. Such magnetic fields are called primordial magnetic fields (PMFs), and are considered to affect the evolution of matter density fluctuations and the thermal history of the IGM gas. Hence the information of PMFs is expected to be imprinted on the anisotropies of the cosmic microwave background (CMB) through the thermal Sunyaev-Zel'dovich (tSZ) effect in the IGM. In this study, given an initial power spectrum of PMFs as $P(k)\propto B_{\rm 1Mpc}^2 k^{n_{B}}$, we calculate dynamical and thermal evolutions of the IGM under the influence of PMFs, and compute the resultant angular power spectrum of the Compton $y$-parameter on the sky. As a result, we find that two physical processes driven by PMFs dominantly determine the power spectrum of the Compton $y$-parameter; (i) the heating due to the ambipolar diffusion effectively works to increase the temperature and the ionization fraction, and (ii) the Lorentz force drastically enhances the density contrast just after the recombination epoch. These facts result in making the tSZ angular power spectrum induced by the PMFs more remarkable at $\ell >10^4$ than that by galaxy clusters even with $B_{\rm 1Mpc}=0.1$ nG and $n_{B}=-1.0$ because the contribution from galaxy clusters decreases with increasing $\ell$. The measurement of the tSZ angular power spectrum on high $\ell$ modes can provide the stringent constraint on PMFs.

astro-ph.CO↗

arXiv2018

Thermal Sunyaev-Zel'dovich Effect in the IGM due to Primordial Magnetic Fields

In the present universe, magnetic fields exist with various strengths and on various scales. One possible origin of these cosmic magnetic fields is the primordial magnetic fields (PMFs) generated in the early universe. PMFs are considered to contribute to matter density evolution via Lorentz force and the thermal history of intergalactic medium (IGM) gas due to ambipolar diffusion. Therefore, information about PMFs should be included in the temperature anisotropy of the Cosmic Microwave Background through the thermal Sunyaev-Zel'dovich (tSZ) effect in IGM. In this article, given an initial power spectrum of PMFs, we show the spatial fluctuation of mass density and temperature of the IGM and tSZ angular power spectrum created by the PMFs. Finally, we find that the tSZ angular power spectrum induced by PMFs becomes significant on small scales, even with PMFs below the observational upper limit. Therefore, we conclude that the measurement of tSZ anisotropy on small scales will provide the most stringent constraint on PMFs.

astro-ph.CO↗

arXiv2018

Limits on primordial magnetic fields from direct detection experiments of gravitational wave background

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 ($>1 {\rm Mpc}$), 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 $10^{2} {\rm nG}$ on much smaller scales of about $k\approx 10^{12} {\rm Mpc}^{-1}$. 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 $30 {\rm nG}$ whose coherent length is of about $k\approx 10^{6} {\rm Mpc}^{-1}$. The future experiments for the direct detection of GWB by the Square Kilometre Array could give much tighter constraints on the amplitude of PMFs about $5 {\rm nG}$ on $k\approx 10^{6} {\rm Mpc}^{-1}$, on which scales, it is difficult to reach by using the cosmological observations.

astro-ph.CO↗

arXiv2018

Probing primordial non-Gaussianity with 21 cm fluctuations from minihalos

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 parameters $τ_{\rm NL}$ and $g_{\rm NL}$. We show that future measurements of minihalo 21 cm angular power spectrum can probe these non-linearity parameters with an unprecedented precision of $τ_{\rm NL}\sim30$ and $g_{\rm NL}\sim2\times10^3$ for Square Kilometre Array (SKA) and $τ_{\rm NL}\sim0.6$ and $g_{\rm NL}\sim8\times10^2$ 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.

astro-ph.CO↗

arXiv2018

Matter bispectrum beyond Horndeski

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 ($k_1+k_2=k_3$), while it is never possible within the Horndeski theory.

astro-ph.CO↗

arXiv2018

The radio telescope search for the resonant conversion of cold dark matter axions from the magnetized astrophysical sources

We study the conditions for the adiabatic resonant conversion of the cold dark matter (CDM) axions into photons in existence of the astrophysically sourced strong magnetic fields such as those in the neutron star magnetosphere. We demonstrate the possibility that the forthcoming radio telescopes such as the SKA (Square Kilometre Array) can probe those photon signals from the CDM axions.

hep-ph↗

arXiv2017

Magnetic reheating

We provide a new bound on the amplitude of primordial magnetic fields (PMFs) by using a novel mechanism, named {\it magnetic reheating}. Before the epoch of recombination, PMFs induce the fluid motions in a photon-baryon plasma through the Lorentz force. Due to the viscosity in the plasma, such induced fluid motions would be damped and this means the dissipation of PMFs. In the early Universe with $z \gtrsim 2 \times 10^6$, 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 energy injection due to the dissipation of PMFs changes the baryon-photon number ratio during this era and we name such a process {\it magnetic reheating}. By using the current results of the baryon-photon number ratio obtained from the Big Bang nucleosynthesis and CMB observations, we put a strongest constraint on the amplitude of PMFs on small scales which we can not access through CMB anisotropy and CMB distortions, $B_{0} \lesssim 1.0 \; μ{\rm G}$ at the scales $10^{4} \; h{\rm Mpc}^{-1} < k < 10^{8} \; h{\rm Mpc}^{-1}$. Moreover, when the spectrum of PMFs is given by the power-law, the magnetic reheating puts a quite strong constraint in the case of the blue-tilted spectrum, for example, $B_0 \lesssim 10^{-17} \;{\rm nG}$, $10^{-23} \;{\rm nG}$, and $10^{-29} \;{\rm nG}$ at 1~comoving Mpc for $n_{B}=1.0$, $2.0$, and $3.0$, respectively. This constraint would give an impact on generation mechanisms of PMFs in the early Universe.

astro-ph.CO↗