arXiv subjects

Dai G. Yamazaki

Publications and source records attributed to Dai G. Yamazaki.

17 recordsLinked to original sources

arXiv2018

Impact of a primordial magnetic field on cosmic microwave background $B$ modes with weak lensing

We discuss the manner in which the primordial magnetic field (PMF) suppresses the cosmic microwave background (CMB) $B$ mode due to the weak-lensing (WL) effect. The WL effect depends on the lensing potential (LP) caused by matter perturbations, the distribution of which at cosmological scales is given by the matter power spectrum (MPS). Therefore, the WL effect on the CMB $B$ mode is affected by the MPS. Considering the effect of the ensemble average energy density of the PMF, which we call "the background PMF," on the MPS, the amplitude of MPS is suppressed in the wave number range of $k>0.01~h$ Mpc$^{-1}$.The MPS affects the LP and the WL effect in the CMB $B$ mode; however, the PMF can damp this effect. Previous studies of the CMB $B$ mode with the PMF have only considered the vector and tensor modes. These modes boost the CMB $B$ mode in the multipole range of $\ell > 1000$, whereas the background PMF damps the CMB $B$ mode owing to the WL effect in the entire multipole range. The matter density in the Universe controls the WL effect. Therefore, when we constrain the PMF and the matter density parameters from cosmological observational data sets, including the CMB $B$ mode, we expect degeneracy between these parameters. The CMB $B$ mode also provides important information on the background gravitational waves, inflation theory, matter density fluctuations, and the structure formations at the cosmological scale through the cosmological parameter search. If we study these topics and correctly constrain the cosmological parameters from cosmological observations including the CMB $B$ mode, we need to correctly consider the background PMF.

astro-ph.CO↗

arXiv2017

Cosmic Magnetism in Centimeter and Meter Wavelength Radio Astronomy

Magnetic field is ubiquitous in the Universe and it plays essential roles in various astrophysical phenomena, yet its real origin and evolution are poorly known. This article reviews current understanding of magnetic fields in the interstellar medium, the Milky Way Galaxy, external galaxies, active galactic nuclei, clusters of galaxies, and the cosmic web. Particularly, the review concentrates on the achievements that have been provided by centimeter and meter wavelength radio observations. The article also introduces various methods to analyze linear polarization data, including synchrotron radiation, Faraday rotation, depolarization, and Faraday tomography.

astro-ph.HE↗

arXiv2016

Evolution of the cosmic matter density field with a primordial magnetic field

A cosmological magnetic field affects the time evolution of the cosmic matter density field. The squared Alfven velocity of the cosmic fluid is proportional to an ensemble average energy density of a primordial magnetic field (PMF), and it prevents the matter density field from collapsing in the horizon scale. The matter-radiation equality time also is delayed by the presence of an ensemble average energy density of a PMF. The ensemble average energy density of the PMF also affects the matter power spectrum (MPS) through the Meszaros effect and the potential decay. Since the ensemble average energy density of the PMF is not a first order perturbation but a zero order source in the linear perturbation equations for the cosmology, to correctly understand the overall effects of the PMF on the MPS, we should significantly revise previous approaches to research for the MPS with the PMF by considering both the effects of the zero and first order sources from the PMF in the linear perturbation theory. We apply the effects of the zero order sources from the PMF to theoretical computations of the MPS for the first time. We also analyze the overall PMF effects on the MPS. The CMB polarizations are affected the weak lensing. The weak lensing is determined by the MPS. Therefore, we have to consider the zero order sources of the PMF to gain a correct understanding not only of the MPS but also the CMB polarization.

astro-ph.CO↗

arXiv2014

Cosmological solutions to the Lithium problem: Big-bang nucleosynthesis with photon cooling, $X$-particle decay and a primordial magnetic field

The $^7$Li abundance calculated in BBN with the baryon-to-photon ratio fixed from fits to the CMB power spectrum is inconsistent with the observed lithium abundances on the surface of metal-poor halo stars. Previous cosmological solutions proposed to resolve this $^7$Li problem include photon cooling (possibly via the Bose-Einstein condensation of a scalar particle) or the decay of a long-lived $X-$particle (possibly the next-to-lightest supersymmetric particle). In this paper we reanalyze these solutions, both separately and in concert. We also introduce the possibility of a primordial magnetic field (PMF) into these models. We constrain the $X-$particles and the PMF parameters by the observed light element abundances using a likelihood analysis to show that the inclusion of all three possibilities leads to an optimum solution to the lithium problem. We deduce allowed ranges for the $X-$particle parameters and energy density in the PMF that can solve $^7$Li problem.

astro-ph.CO↗

arXiv2014

CMB with the background primordial magnetic field

We investigate the effects of the background primordial magnetic field (PMF) on the cosmic microwave background (CMB). The sound speed of the tightly coupled photon-baryon fluid is increased by the background PMF. The increased sound speed causes the odd peaks of the CMB temperature fluctuations to be suppressed and the CMB peak positions to be shifted to a larger scale. The background PMF causes a stronger decaying potential and increases the amplitude of the CMB. These two effects of the background PMF on a smaller scale cancel out, and the overall effects of the background PMF are the suppression of the CMB around the first peak and the shifting of peaks to a large scale. We also discuss obtaining information about the PMF generation mechanisms, and we examine the nonlinear evolution of the PMF by the constraint on the maximum scale for the PMF distributions. Finally, we discuss degeneracies between the PMF parameters and the standard cosmological parameters.

astro-ph.CO↗

arXiv2013

Constraints on the multi-lognormal magnetic fields from the observations of the cosmic microwave background and the matter power spectrum

Primordial magnetic fields (PMFs), which were generated in the early Universe before recombination, affect the motion of plasma and then the cosmic microwave background and the matter power spectrum. We consider constraints on PMFs with a characteristic correlation length from the observations of the anisotropies of the cosmic microwave background and the matter power spectrum. The spectrum of PMFs is modeled with multi-lognormal distributions, rather than power-law distribution, and we derive constraints on the strength $|\mathbf{B}_k|$ at each wave number $k$ along with the standard cosmological parameters in the flat Universe and the foreground sources. We obtain upper bounds on the field strengths at $k=10^{-1}, 10^{-2}, 10^{-4}$, and $10^{-5}$ Mpc$^{-1}$ as 4.7 nG, 2.1 nG, 5.3 nG, and 10.9 nG ($2σ$ C.L.) respectively, while the field strength at $k=10^{-3} $Mpc$^{-1}$ turns out to have a finite value as $|\mathbf{B}_{k = 10^{-3}}| = 6.2 \pm 1.3 $ nG ($1σ$ C.L.). This finite value is attributed to the finite values of BB mode data at $\ell > 300$ obtained from the QUAD experiment. If we do not include the BB mode data, we obtain only the upper bound on $B_{k=10^{-3}}$.

astro-ph.CO↗

arXiv2012

Effects of power law primordial magnetic field on big bang nucleosynthesis

Big bang nucleosynthesis (BBN) is affected by the energy density of a primordial magnetic field (PMF). For an easy derivation of constraints on models for PMF generations, we assume a PMF with a power law (PL) distribution in wave number defined with a field strength, a PL index, and maximum and minimum scales at a generation epoch. We then show a relation between PL-PMF parameters and the scale invariant (SI) strength of PMF for the first time. We perform a BBN calculation including PMF effects, and show abundances as a function of baryon to photon ratio $η$. The SI strength of the PMF is constrained from observational constraints on abundances of $^4$He and D. The minimum abundance of $^7$Li/H as a function of $η$ slightly moves to a higher $^7$Li/H value at a larger $η$ value when a PMF exists during BBN. We then discuss degeneracies between the PL-PMF parameters in the PMF effect. In addition, we assume a general case in which both the existence and the dissipation of PMF are possible. It is then found that an upper limit on the SI strength of the PMF can be derived from a constraint on $^4$He abundance, and that a lower limit on the allowed $^7$Li abundance is significantly higher than those observed in metal-poor stars.

astro-ph.CO↗

arXiv2012

The Search for a Primordial Magnetic Field

Magnetic fields appear wherever plasma and currents can be found. As such, they thread through all scales in Nature. It is natural, therefore, to suppose that magnetic fields might have been formed within the high temperature environments of the big bang. Such a primordial magnetic field (PMF) would be expected to arise from and/or influence a variety of cosmological phenomena such as inflation, cosmic phase transitions, big bang nucleosynthesis, the cosmic microwave background (CMB) temperature and polarization anisotropies, the cosmic gravity wave background, and the formation of large-scale structure. In this review, we summarize the development of theoretical models for analyzing the observational consequences of a PMF. We also summarize the current state of the art in the search for observational evidence of a PMF. In particular we review the framework needed to calculate the effects of a PMF power spectrum on the CMB and the development of large scale structure. We summarize the current constraints on the PMF amplitude $B_λ$ and the power spectral index $n_B$ and discuss prospects for better determining these quantities in the near future.

astro-ph.CO↗

arXiv2011

Effects of a primordial magnetic field with log-normal distribution on the cosmic microwave background

We study the effect of primordial magnetic fields (PMFs) on the anisotropies of the cosmic microwave background (CMB). We assume the spectrum of PMFs is described by log-normal distribution which has a characteristic scale, rather than power-law spectrum. This scale is expected to reflect the generation mechanisms and our analysis is complementary to previous studies with power-law spectrum. We calculate power spectra of energy density and Lorentz force of the log-normal PMFs, and then calculate CMB temperature and polarization angular power spectra from scalar, vector, and tensor modes of perturbations generated from such PMFs. By comparing these spectra with WMAP7, QUaD, CBI, Boomerang, and ACBAR data sets, we find that the current CMB data set places the strongest constraint at $k\simeq 10^{-2.5}$ Mpc$^{-1}$ with the upper limit $B\lesssim 3$ nG.

astro-ph.CO↗

arXiv2011

Primordial Magnetic Field Effects on the CMB and Large Scale Structure

Magnetic fields are everywhere in nature and they play an important role in every astronomical environment which involves the formation of plasma and currents. It is natural therefore to suppose that magnetic fields could be present in the turbulent high temperature environment of the big bang. Such a primordial magnetic field (PMF) would be expected to manifest itself in the cosmic microwave background (CMB) temperature and polarization anisotropies, and also in the formation of large- scale structure. In this review we summarize the theoretical framework which we have developed to calculate the PMF power spectrum to high precision. Using this formulation, we summarize calculations of the effects of a PMF which take accurate quantitative account of the time evolution of the cut off scale. We review the constructed numerical program, which is without approximation, and an improvement over the approach used in a number of previous works for studying the effect of the PMF on the cosmological perturbations. We demonstrate how the PMF is an important cosmological physical process on small scales. We also summarize the current constraints on the PMF amplitude $B_λ$ and the power spectral index $n_B$ which have been deduced from the available CMB observational data by using our computational framework.

astro-ph.CO↗

arXiv2010

Constraints on the neutrino mass and the primordial magnetic field from the matter density fluctuation parameter $σ_8$

We have made an analysis of limits on the neutrino mass based upon the formation of large-scale structure in the presence of a primordial magnetic field. We find that a new upper bound on the neutrino mass is possible based upon fits to the cosmic microwave background and matter power spectrum when the existing independent constraints on the matter density fluctuation parameter $σ_8$ and the primordial magnetic field are taken into account.

astro-ph.CO↗

arXiv2010

New Constraints on the Primordial Magnetic Field

We present the newest statistical and numerical analysis of the matter and cosmic microwave background power spectrum with effects of the primordial magnetic field (PMF) included. New limits to the PMF strength and power spectral index are obtained based upon the accumulated data for both the matter and CMB power spectra on small angular scales. We find that a maximum develops in the probability distribution for a magnitude of the PMF of $|B_λ| = 0.85 \pm 1.25(\pm 1σ)$ nG on a comoving scale of at 1 Mpc, corresponding to upper limits of $\mathbf{< 2.10 nG} (68% \mathrm{CL})$ and $\mathbf{< 2.98 nG} (95% \mathrm{CL})$. While for the power spectral index we find $n_\mathrm{B}= -2.37^{+0.88}_{-0.73}(\pm 1σ)$, corresponding to upper limits of $ \mathbf{< -1.19} (68% \mathrm{CL})$ and $ \mathbf{< -0.25} (95% \mathrm{CL})$. This result provides new constraints on models for magnetic field generation and the physics of the early universe. We conclude that future observational programs for the CMB and matter power spectrum will likely provide not only upper limits but also lower limits to the PMF parameters.

astro-ph.CO↗

arXiv2008

Constraints on the Primordial Magnetic Field from $σ_8$

A primordial magnetic field (PMF) can affect the evolution of density field fluctuations in the early universe.In this paper we constrain the PMF amplitude $B_λ$ and power spectral index $n_\mathrm{B}$ by comparing calculated density field fluctuations with observational data, i.e. the number density fluctuation of galaxies.We show that the observational constraints on cosmological density fluctuations, as parameterized by $σ_8$, lead to strong constraints on the amplitude and spectral index of the PMF.

astro-ph↗

arXiv2008

Neutrino mass effects on vector and tensor CMB anisotropies in the presence of a primordial magnetic field

If a primordial magnetic field (PMF) is present during photon decoupling and afterward, a finite neutrino mass can affect all modes of the CMB. In this work, we expand on earlier studies of the scalar mode effects by constructing the vector and tensor mode equations in the presence of massive neutrinos and a PMF. We compute the power spectrum of the various modes in an illustrative example and find that the neutrino mass can significantly affect the vector and tensor modes when a PMF exists, while the effects are negligible for no PMF. The most prominent result of the present analysis is the behavior of the EE component of the tensor mode at low multipoles. For massive neutrinos the EE mode can become comparable to the observed primary anisotropy. Therefore, if and when the EE mode power spectrum is measured at low multipoles the possibility exists to place a strong constraint on the sum of the neutrino masses.

astro-ph↗

arXiv2008

Effects of a Primordial Magnetic Field on Low and High Multipoles of the CMB

The existence of a primordial magnetic field (PMF) would affect both the temperature and polarization anisotropies of the cosmic microwave background (CMB). It also provides a plausible explanation for the possible disparity between observations and theoretical fits to the CMB power spectrum. Here we report on calculations of not only the numerical CMB power spectrum from the PMF, but also the correlations between the CMB power spectrum from the PMF and the primary curvature perturbations. We then deduce a precise estimate of the PMF effect on all modes of perturbations. We find that the PMF affects not only the CMB TT and TE modes on small angular scales, but also on large angular scales. The introduction of a PMF leads to a better fit to the CMB power spectrum for the higher multipoles, and the fit at lowest multipoles can be used to constrain the correlation of the PMF with the density fluctuations for large negative values of the spectral index. Our prediction for the BB mode for a PMF average field strength $|B_λ| =4.0$ nG is consistent with the upper limit on the BB mode deduced from the latest CMB observations. We find that the BB mode is dominated by the vector mode of the PMF for higher multipoles. We also show that by fitting the complete power spectrum one can break the degeneracy between the PMF amplitude and its power spectral index.

astro-ph↗

arXiv2006

Effect of Primordial Magnetic Field on Seeds for Large Scale Structure

Magnetic field plays a very important role in many astronomical phenomena at various scales of the universe. It is no exception in the early universe. Since the energy density, pressure, and tension of the primordial magnetic field affect gravitational collapses of plasma, the formation of seeds for large scale structures should be influenced by them. Here we numerically investigate the effects of stochastic primordial magnetic field on the seeds of large scale structures in the universe in detail. We found that the amplitude ratio between the density spectra with and without PMF ($|P(k)/P_0(k)|$ at $k>0.2$ Mpc$^{-1}$) lies between 75% and 130% at present for the range of PMF strengths 0.5 nG $< B_λ< 1.0$ nG, depending on the spectral index of PMF and the correlation between the matter density and the PMF distributions.

astro-ph↗

arXiv2006

Primordial magnetic field constrained from CMB anisotropies,and its generation and evolution before, during and after the BBN

The primordial magnetic field (PMF) can strongly affect the cosmic microwave background (CMB) power spectrum and the formation of large scale structure. In this presentation, we calculate the CMB temperature anisotropies generated by including a power-law magnetic field at the photon last scattering surface (PLSS). We then deduce an upper limit on the primordial magnetic field based upon our theoretical analysis of the power excess on small angular scales. We have taken into account several important effects such as the modified matter sound speed in the presence of a magnetic field. An upper limit to the field strength of $|B_λ|\lesssim$ 4.7 nG at the present scale of 1 Mpc is deduced. This is obtained by comparing the calculated theoretical result including the Sunyaev-Zeldovich (SZ) effect with recent observed data on the small scale CMB anisotropies from the Wilkinson Microwave Anisotropy Probe (WMAP), the Cosmic Background Imager (CBI) and the Arcminute Cosmology Bolometer Array Receiver (ACBAR). We discuss several possible mechanisms for the generation and evolution of the PMF before, during and after the BBN.

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