arXiv subjects

Kenji Tomita

Publications and source records attributed to Kenji Tomita.

At least 19 recordsLinked to original sources

arXiv2020

Hubble constants and luminosity distance in the renormalized cosmological models due to general-relativistic second-order perturbations

Renormalized cosmological models based on the general-relativistic second-order perturbation theory were proposed in the previous papers to solve a tension on the observed Hubble constants. The cosmological random adiabatic fluctuations were found to play an important role as the first-order perturbations. The second-order metric perturbations in a previous paper are revised in the present paper. It is shown as a result that two types of Hubble constants (the kinematic constant H_kin and the dynamic constant H_dyn) are derived, and their values are found to be comparable, and larger than the background value. The optical quantities such as redshift and luminosity distance are derived using the revised metric perturbations.

gr-qc↗

arXiv2018

Super-horizon second-order perturbations for cosmological random fluctuations and the Hubble-constant problem

The super-horizon second-order density perturbations corresponding to cosmological random fluctuations are considered, their non-vanishing spatial average is shown to be useful in solving the serious problem on the cosmological tension between measured Hubble constants at present and those at the early stage, and the difference from previous works on the backreaction is discussed.

astro-ph.CO↗

arXiv2017

Cosmological models with the energy density of random fluctuations and the Hubble-constant problem

First the fluctuation energy is derived from the adiabatic random fluctuations due to the second-order perturbation theory, and the evolutionary relation for it is expressed in the form of rho_f = rho_f (rho), where rho and rho_f are the densities of ordinary dust and the fluctuation energy, respectively. The pressureless matter as a constituent of the universe at the later stage is assumed to consist of ordinary dust and the fluctuation energy. Next, cosmological models including the fluctuation energy as a kind of dark matter are derived using the above relation, and it is found that the Hubble parameter and the other model parameters in the derived models can be consistent with the recent observational values. Moreover, the perturbations of rho and rho_f are studied.

gr-qc↗

arXiv2017

Cosmological renormalization of model parameters in the second-order perturbation theory

It is shown that the serious problem on the cosmological tension between the direct measurements of the Hubble constant at present and the constant derived from the Planck measurements of the CMB anisotropies can be solved by considering the renormalized model parameters. They are deduced by taking the spatial average of second-order perturbations in the flat Lambda-CDM model, which includes random adiabatic fluctuations.

astro-ph.CO↗

arXiv2016

Note on Nariai and Tomita's and Starobinsky's cosmological solutions in the R^2 modified gravity

Cosmological solutions derived by Nariai and Tomita (1971) and by Starobinsky (1980) are compared, and it is shown that the former derived de Sitter expansion in the R^2 modified gravity (without cosmological constant) at the earliest stage, and nine years later the latter derived the well-known inflationary solution. Next the property of their simplified models is described using the method of conformal transformations, and how the inflation arises and the singularity is avoided is shown. Finally the initial and final states of the inflation are discussed.

gr-qc↗

arXiv2015

Fluctuations of the cosmic background radiation appearing in the 10-dimensional cosmological model

We consider a cosmological model starting from (1) the(1+3+6)-dimensional space-times consisting of the outer space (the 3-dimensional expanding section) and the inner space (the 6-dimensional section) and reaching (2) the Friedmann model after the decoupling between the outer space and the inner space, and derive fluctuations of the background radiation appearing in the above 10-dimensional space-times. For this purpose we first derive the fluid-dynamical perturbations in the above 10-dimensional space-times, corresponding to two kinds of curvature perturbations (in the scalar mode) in the non-viscous case, and next study the quantum fluctuations in the scalar and tensor modes, appearing at the stage when the perturbations are within the horizon of the inflating outer space. Lastly we derive the wave-number dependence of fluctuations (the power spectrum) in the two modes, which formed at the above decoupling epoch and are observed in the Friedmann stage. It is found that it can be consistent with the observed spectra of the cosmic microwave background radiation.

gr-qc↗

arXiv2014

Cosmological perturbations in the (1+3+6)-dimensional space-times

Cosmological perturbations in the (1+3+6)-dimensional space-times including photon gas without viscous processes are studied on the basis of Abbott et al.'s formalism. Space-times consist of the outer space (the 3-dimensional expanding section) and the inner space (the 6-dimensional section). The inner space expands initially and contracts later. Abbott et al. derived only power-type solutions in the small wave-number limit which appear at the final stage of the space-times. In this paper, we derive not only small wave-number solutions, but also large wave-number solutions. It is found that the latter solutions depend on the two wave-numbers k_r and k_R (which are defined in the outer and inner spaces, respectively), and that the k_r-dependent and k_R-dependent parts dominate the total perturbations when (k_r/r(t))/(k_R/R(t)) >> 1 or << 1, respectively, where r(t) and R(t) are the scale-factors in the outer and inner spaces. By comparing the behaviors of these perturbations, moreover, changes in the spectrum of perturbations in the outer space with time are discussed.

gr-qc↗

arXiv2014

Cosmological entropy production and viscous processes in the (1+3+6)-dimensional space-times

The cosmological entropy production is studied in the (1+3+6)-dimensional space-times consisting of the outer space (the 3-dimensional expanding section) and the inner space (the 6-dimensional section). The inner space expands initially and contracts later. First it is shown how the production of the 3-dimensional entropy S_3 within the horizon is strengthened by the dissipation due to viscous processes between the two spaces, in which we consider the viscosity caused by the gravitational-wave transport. Next it is shown under what conditions we can have the critical epoch when S_3 reaches the value 10^{88} in the Guth level and at the same time the outer space is decoupled from the inner space. Moreover, the total entropy S_9 in the 9-dimensional space at the primeval expanding stage is also shown corresponding to S_3.

gr-qc↗

arXiv2014

Cosmological entropy problem in the (1+3+6)-dimensional space-times with viscous processes

Recently the formation of an expanding universe from the (1+3+6)-dimensional space-times has been proposed on the basis of super-string theory. The serious entropy problem must be solved for it to be realistic from the cosmological viewpoint. It is discussed here, taking account of the large dissipation due to the viscous motion between the collapsing inner space and the inflating outer space. It is shown that the large dissipation may be effective for the vast production of 3-dimensional entropy S_3 within the horizon, and that there are epochs when S_3 reaches the critical value 10^88 in the Guth level and at the same time the outer space is decoupled from the inner space.

gr-qc↗

arXiv2010

Evidence of Quasi-linear Super-Structures in the Cosmic Microwave Background and Galaxy Distribution

Recent measurements of hot and cold spots on the cosmic microwave background (CMB) sky suggest a presence of super-structures on (>100 h^{-1}Mpc) scales. We develop a new formalism to estimate the expected amplitude of temperature fluctuations due to the integrated Sachs-Wolfe (ISW) effect from prominent quasi-linear structures. Applying the developed tools to the observed ISW signals from voids and clusters in catalogs of galaxies at redshifts z<1, we find that they indeed imply a presence of quasi-linear super-structures with a comoving radius 100~300 h^{-1}Mpc and a density contrast ~O(0.1). We find that the observed ISW signals are at odd with the concordant Λcold dark matter (CDM) model that predicts Gaussian primordial perturbations at equal to or larger than 3 sigma level. We also confirm that the mean temperature around the CMB cold spot in the southern Galactic hemisphere filtered by a compensating top-hat filter deviates from a mean value at ~3 sigma level, implying that a quasi-linear supervoid or an underdensity region surrounded by a massive wall may reside at low redshifts z<0.3 and the actual angular size (16^\circ-17^\circ) may be larger than the apparent size (4^\circ-10^\circ) discussed in literature. Possible solutions are briefly discussed.

astro-ph.CO↗

arXiv2010

Gauge-invariant treatment of the integrated Sachs-Wolfe effect on general spherically symmetric spacetimes

On the basis of the Gerlach-Sengupta theory of gauge-invariant perturbations, a formula of the integrated Sachs-Wolfe effect for a central observer is derived on general spherically symmetric spacetimes. It will be useful for comparative studies of theoretical and observational aspects of the integrated Sachs-Wolfe effect in the Lemaitre-Tolman-Bondi cosmological models which have been noticed by explaining the apparent acceleration without cosmological constant.

astro-ph.CO↗

arXiv2009

On astrophysical explanations due to cosmological inhomogeneities for the observational acceleration

We review various cosmological models with a local underdense region (local void) and the averaged models with the backreaction of inhomogeneities, which have been proposed to explain (without assuming a positive cosmological constant) the observed accelerating behaviors appearing in the magnitude-redshift relation of SNIa. To clarify their reality, we consider their consistency with the other observational studies such as CMB temperature anisotropy, baryon acoustic oscillation, kinematic Sunyaev-Zeldovich effect, and so on. It is found as a result that many inhomogeneous models seem to be ruled out and only models with the parametrs in the narrow range remain to be examined, and that, unless we assume very high amplitudes of perturbations or gravitational energies, the averaged models cannot have the accelerated expansion and the fitted effective Lambda has not the value necessary for the observed acceleration.

astro-ph.CO↗

arXiv2009

Probing violation of the Copernican principle via the integrated Sachs-Wolfe effect

Recent observational data of supernovae indicate that we may live in an underdense region, which challenges the Copernican principle. We show that the integrated Sachs-Wolfe (ISW) effect is an excellent discriminator between anti-Copernican inhomogeneous models and the standard Copernican models. As a reference model, we consider an anti-Copernican inhomogeneous model that consists of two inner negatively curved underdense regions and an outer flat Einstein-de Sitter region. We assume that these regions are connected by two thin-walls at redshifts z = 0.067 and z=0.45. In the inner two regions, the first-order ISW effect is dominant and comparable to that in the concordant flat-Lambda models. In the outer Einstein-de Sitter region, the first-order ISW effect vanishes but the second-order ISW effect plays a dominant role, while the first-order ISW effect is dominant in the flat-Lambda models at moderate redshifts. This difference can discrimate the anti-Copernican models from the concordant flat-Lambda model. At high redshits, the second-order ISW effect is dominant both in our inhomogeneous model and the concordant model. In the outer region, moreover, the ISW effect due to large-scale density perturbations with a present matter density contrast much less than 0.37 is negligible, while the effect due to small-scale density perturbations (such as clusters of galaxies, superclusters and voids) with matter density contrast much larger than 0.37 would generate anisotropies which are larger than those generated by the ISW effect in the concordant model.

astro-ph.CO↗

arXiv2008

Second-order power spectra of CMB anisotropies due to primordial random perturbations in flat cosmological models

Second-order power spectra of Cosmic Microwave Background (CMB) anisotropies due to random primordial perturbations at the matter dominant stage are studied, based on the relativistic second-order theory of perturbations in flat cosmological models and on the second-order formula of CMB anisotropies derived by Mollerach and Matarrese. So far the second-order integrated Sachs-Wolfe effect has been analyzed using the three-point correlation or bispectrum. In this paper we derive the second-order term of power spectra given using the two-point correlation of temperature fluctuations. The second-order density perturbations are small, compared with the first-order ones. The second-order power spectra of CMB anisotropies, however, are not small at all, compared with the first-order power spectra, because at the early stage the first-order integrated Sachs-Wolfe effect is very small and the second-order integrated Sachs-Wolfe effect may be dominant over the first-order ones. So their characteristic behaviors may be measured through the future precise observation and bring useful informations on the structure and evolution of our universe in the future.

astro-ph↗

arXiv2008

Second Order Gravitational Effects on CMB Temperature Anisotropy in Lambda dominated flat universes

We study second order gravitational effects of local inhomogeneities on the cosmic microwave background radiation in flat universes with matter and a cosmological constant $Λ$. We find that the general relativistic correction to the Newtonian approximation is negligible at second order provided that the size of the inhomogeneous region is sufficiently smaller than the horizon scale. For a spherically symmetric top-hat type quasi-linear perturbation, the first order temperature fluctuation corresponding to the linear integrated Sachs-Wolfe (ISW) effect is enhanced(suppressed) by the second order one for a compensated void(lump). As a function of redshift of the local inhomogeneity, the second order temperature fluctuations due to evolution of the gravitational potential have a peak before the matter-$Λ$ equality epoch for a fixed comoving size and a density contrast. The second order gravitational effects from local quasi-linear inhomogeneities at a redshift z~1 may significantly affect the cosmic microwave background.

astro-ph↗

arXiv2006

Second-order gravitational effects of local inhomogeneities on CMB anisotropies in nonzero-Lambda flat cosmological models

Nonlinear gravitational effects of large-scale inhomogeneities on Cosmic Microwave Background (CMB) anisotropies are studied. based on the relativistic second-order theory of perturbations in nonzero-Lambda flat cosmological models, which has been analytically derived by the present author, and on the second-order formula of CMB anisotropies derived by Mollerach and Matarrese. In this paper we derive the components of the CMB anisotropy power spectra in the range of l = 1 -22 which are caused by asymmetric local inhomogeneities on scales of 300 Mpc. Using our results it is found that there is a possibility to explain the small north-south asymmetry of CMB anisotropies which has recently been observed.

astro-ph↗

arXiv2006

Second-order gravitational effects of local inhomogeneities on CMB anisotropies and non-Gaussian signatures

Based on the second-order nonlinear theory of perturbations in non-zero Λflat cosmological models, we study the gravitational effects of local inhomogeneities on cosmic microwave background (CMB) anisotropies. As the local inhomogeneities we consider firstly large-scale dipole and quadruple distributions of galaxies around us and next an isolated cluster-scale matter distribution. It is found that, due to the second-order integral Sachs-Wolfe effect, the north-south asymmetry of CMB anisotropies and non-Gaussian signatures (in terms of scale-dependent estimators of kurtosis) in a spot-like object are caused from these matter distributions along light paths. Our theoretical results seem to be consistent with recent various observational results which have been shown by Hansen et al., Eriksen et al., Vielva et al. and Cruz et al.

astro-ph↗

arXiv2005

Relativistic second-order perturbations of nonzero-Λflat cosmological models and CMB anisotropies

First the second-order perturbations of nonzero-Λcosmological models are derived with an arbitrary potential function of spatial coordinates, using the nonlinear version of Lifshitz's method in the synchronous gauge. Their expression is the generalization (to the nonzero-Λcase) of second-order perturbations in the Einstein-de Sitter model which were derived previously by the present author. Next the second-order temperature anisotropies of Cosmic Micriwave Background radiation are derived using the gauge-invariant formula which was given by Mollerach and Matarrese. Moreover the corresponding perturbations in the Poisson gauge are derived using the second-order gauge transformations formulated by Bruni et al. In the second-order it is found in spite of gauges that tensor (gravitational-wave) perturbations and vector (shear) perturbations without vorticity are induced from the first-order scalar perturbations. These results will be useful to analyze the nonlinear effect of local inhomogeneities on Cosmic Microwave Background anisotropies.

astro-ph↗