arXiv subjects

Naoshi Sugiyama

Publications and source records attributed to Naoshi Sugiyama.

At least 127 records · Page 7Linked to original sources

arXiv1999

The Sunyaev-Zel'dovich Effect by Cocoons of Radio Galaxies

We estimate the deformation of the cosmic microwave background radiation by the hot region (``cocoon'') around a radio galaxy. A simple model is adopted for cocoon evolution while the jet is on, and a model of evolution is constructed after the jet is off. It is found that at low redshift the phase after the jet is off is longer than the lifetime of the jets. The Compton y-parameter generated by cocoons is calculated with a Press-Schechter number density evolution. The resultant value of y is of the same order as the COBE constraint. The Sunyaev-Zeldovich effect due to cocoons could therefore be a significant foreground source of small angular scale anisotropies in the cosmic microwave background radiation.

astro-ph↗

arXiv1999

Limits on Neutrino Mass from Cosmic Structure Formation

We consider the effect of three species of neutrinos with nearly degenerate mass on the cosmic structure formation in a low matter-density universe within a hierarchical clustering scenario with a flat initial perturbation spectrum. The matching condition for fluctuation powers at the COBE scale and at the cluster scale leads to a strong upper limit on neutrino mass. For a flat universe with matter density parameter Omega=0.3, we obtain m_nu<0.6eV for the Hubble constant H_0<80km/s/Mpc. Allowing for the more generous parameter space limited by Omega<0.4, H_0<80km/s/Mpc and age t_0>11.5Gyr, the limit is 0.9eV.

hep-ph↗

arXiv1999

Observational Implications of Axionic Isocurvature Fluctuations

The axion is the most attractive candidate to solve the strong CP problem in QCD. If it exists, the inflationary universe produces axion fluctuations which are mixtures of isocurvature and adiabatic fluctuations in general. We investigate how large isocurvature fluctuations are allowed or favored in order to explain observations of the large scale structure of the present universe. Generic flat universe models with mixed (isocurvature + adiabatic) density fluctuations are studied. It is found that the observations are consistent with the mixed fluctuation model if the ratio αof the power spectrum of isocurvature fluctuations to that of adiabatic fluctuations is less than \sim 0.1. In particular, the mixed fluctuation model with α\sim 0.05, total matter density Ω_{0} =0.4, and Hubble parameter H_0=70 km/s/Mpc gives a very good fit to the observational data. Since the height of the acoustic peak in the angular power spectrum of the cosmic microwave background (CMB) radiation decreases significantly when the isocurvature fluctuations are present, the mixed fluctuation model can be tested in future satellite experiments. Ratios of the amplitude at the peak location to that at the COBE normalization scale for various models are given. Furthermore, we also obtain the amplitude of isocurvature fluctuations as a function of axion parameters and the Hubble parameter during the inflation. We discuss the axion fluctuations in some realistic inflation models and find that a significant amount of the isocurvature fluctuations are naturally produced.

astro-ph↗

arXiv1999

Cosmological Constraints on Late-time Entropy Production

We investigate cosmological effects concerning the late-time entropy production due to the decay of non-relativistic massive particles. The thermalization process of neutrinos after the entropy production is properly solved by using the Boltzmann equation. If a large entropy production takes place at late time t$\simeq$ 1 sec, it is found that a large fraction of neutrinos cannot be thermalized. This fact loosens the tight constraint on the reheating temperature T_R from the big bang nucleosynthesis and T_R could be as low as 0.5 MeV. The influence on the large scale structure formation and cosmic microwave background anisotropies is also discussed.

astro-ph↗

arXiv1999

Python I, II, and III CMB Anisotropy Measurement Constraints on Open and Flat-Lambda CDM Cosmogonies

We use Python I, II, and III cosmic microwave background anisotropy data to constrain cosmogonies. We account for the Python beamwidth and calibration uncertainties. We consider open and spatially-flat-Lambda cold dark matter cosmogonies, with nonrelativistic-mass density parameter Omega_0 in the range 0.1--1, baryonic-mass density parameter Omega_B in the range (0.005--0.029) h^{-2}, and age of the universe t_0 in the range (10--20) Gyr. Marginalizing over all parameters but Omega_0, the combined Python data favors an open (spatially-flat-Lambda) model with Omega_0 simeq 0.2 (0.1). At the 2 sigma confidence level model normalizations deduced from the combined Python data are mostly consistent with those drawn from the DMR, UCSB South Pole 1994, ARGO, MAX 4 and 5, White Dish, and SuZIE data sets.

astro-ph↗

arXiv1999

CMB Anisotropy Constraints on Open and Flat-Lambda CDM Cosmogonies from UCSB South Pole, ARGO, MAX, White Dish, and SuZIE Data

We use combinations of ten small-scale cosmic microwave background anisotropy data sets from the UCSB South Pole 1994, ARGO, MAX 4 and 5, White Dish and SuZIE experiments to constrain cosmogonies. We consider open and spatially-flat-Lambda cold dark matter cosmogonies. Marginalizing over all parameters but $Ω_0$, the combined data favors an Omega_0 simeq 1 for both open and flat-Lambda models. Excluding the smallest angular scale SuZIE data, an Omega_0 simeq 0.3 (1.0) open (flat-Lambda) model is favored. Considering only multi-frequency data with error bars consistent with sample variance and noise considerations, an Omega_0 simeq 0.1 (1) open (flat-Lambda) model is favored. For both open and flat-$Λ$ models, after marginalizing over all the other parameters, a lower Omega_B h^2 (sim 0.005) or younger (t_0 sim 10 Gyr) universe is favored. However, the data do not rule out other values of Omega_0 in the flat-Lambda model and other values of Omega_B h^2 in both models. (abriged)

astro-ph↗

arXiv1998

Effect of Void Network on CMB Anisotropy

We study the effect of a void network on the CMB anisotropy in the Einstein-de Sitter background using Thompson &Vishniac's model. We consider comprehensively the Sacks-Wolfe effect, the Rees-Sciama effect and the gravitational lensing effect. Our analysis includes the model of primordial voids existing at recombination, which is realized in some inflationary models associated with a first-order phase transition. If there exist primordial voids whose comoving radius is larger than $\sim10h^{-1}$Mpc at recombination, not only the Sachs-Wolfe effect but also the Rees-Sciama effect is appreciable even for multipoles $l\lsim1000$ of the anisotropy spectrum. The gravitational lensing effect, on the other hand, slightly smoothes the primary anisotropy; quantitatively, our results for the void model are similar to the previous results for a CDM model. All the effects, together, would give some constraints on the configuration or origin of voids with high-resolution data of the CMB anisotropy.

astro-ph↗

arXiv1998

Isocurvature Fluctuations of the M-theory Axion in a Hybrid Inflation Model

The M-theory, the strong-coupling heterotic string theory, presents various interesting new phenomenologies. The M-theory bulk axion is one of these. The decay constant in this context is estimated as $F_a\simeq 10^{16}$ GeV. Direct searches for the M-theory axion seem impossible because of the large decay constant. However, we point out that large isocurvature fluctuations of the M-theory axion are obtained in a hybrid inflation model, which will most likely be detectable in future satellite experiments on anisotropies of cosmic microwave background radiation.

hep-ph↗

arXiv1998

Observational tests of x-matter models

We study gravitational lensing statistics, matter power spectra and the angular power spectra of the cosmic microwave background (CMB) radiation in x-matter models. We adopt an equation-of-state of x-matter which can express a wide range of matter from the pressureless dust to the cosmological constant. A new ingredient in this model is the sound speed of the x-component in addition to the equation-of-state $w_0=p_{x0}/ρ_{x0}$. Except for the cosmological constant case, the perturbations of x-matter itself are considered. Our primary interest is in the effect of non-zero sound speed on the structure formation and the CMB spectra. It is found that there exist parameter ranges where x-matter models are consistent with all current observations. The x-matter generally leaves imprints in the CMB anisotropy and the matter power spectrum, which should be detectable in future observations.

astro-ph↗

arXiv1998

ARGO CMB Anisotropy Measurement Constraints on Open and Flat-Lambda CDM Cosmogonies

We use data from the ARGO cosmic microwave background (CMB) anisotropy experiment to constrain cosmogonies. We account for the ARGO beamwidth and calibration uncertainties, and marginalize over the offset removed from the data. Our derived amplitudes of the CMB anisotropy detected by the ARGO experiment are smaller than those derived previously. We consider open and spatially-flat-Lambda cold dark matter cosmogonies, with clustered-mass density parameter Omega_0 in the range 0.1-1, baryonic-mass density parameter Omega_B in the range (0.005-0.029)h^{-2}, and age of the universe t_0 in the range (10--20) Gyr. Marginalizing over all parameters but Omega_0, the ARGO data favors an open (spatially-flat-Lambda) model with Omega_0= 0.23 (0.1). However, these numerical values are model dependent. At the 2 sigma confidence level model normalizations deduced from the ARGO data are consistent with those drawn from the UCSB South Pole 1994, MAX 4+5, White Dish, and SuZIE data sets. The ARGO open model normalizations are also consistent with those deduced from the DMR data. However, for most spatially-flat-Lambda models the DMR normalizations are more than 2 sigma above the ARGO ones.

astro-ph↗

arXiv1998

Small-Scale Fluctuations in Cosmic X-ray Background : A Power Spectrum Approach

Equations to investigate fluctuations in cosmic X-ray background radiation due to point-like sources at high-redshift are formulated in a systematic way. The angular power spectrum of X-ray background fluctuations is investigated from large-scales to small-scales in various cosmological models such as open universe models and models with the cosmological constant, assuming a simple evolution model of the sources. The effect of epoch-dependent bias is demonstrated for small-angle fluctuations. The contribution from shot noise fluctuations is also discussed.

astro-ph↗

arXiv1998

Imprints of the Metrically-coupled Dilaton on Density Perturbations in Inflationary Cosmology

Spectra of density perturbations produced during chaotic inflation are calculated, taking both adiabatic and isocurvature modes into account in a class of scalar-tensor theories of gravity in which the dilaton is metrically coupled. Comparing the predicted spectrum of the cosmic microwave background radiation anisotropies with the one observed by the COBE-DMR we calculate constraints on the parameters of these theories, which turn out to be stronger by an order-of-magnitude than those obtained from post-Newtonian experiments.

gr-qc↗

arXiv1997

CMB Anisotropy Correlation Function and Topology from Simulated Maps for MAP

We have simulated cosmic microwave background (CMB) anisotropy maps for several COBE-DMR-normalized cold dark matter (CDM) cosmogonies, to make predictions for the upcoming MAP experiment. We have studied the sensitivity of the simulated MAP data to cosmology, sky coverage, and instrumental noise. With accurate knowledge of instrumental noise, MAP data will discriminate among the cosmogonies considered, and determine the topology of the initial fluctuations. A correlation function analysis of the simulated MAP data results in a very accurate measurement of the acoustic Hubble radius at decoupling. A low-density open CDM model with Omega_0=0.4 can be distinguished from the Omega_0=1 fiducial CDM model or a Lambda CDM model with > 99% confidence from the location of the acoustic "valley" in the correlation function. A genus analysis of the simulated MAP data indicates that in cosmogonies with Gaussian random-phase initial conditions, a shift of the zero-crossing point of the genus curve near the mean temperature threshold level nu=0 should not exceed |Delta nu| = 0.01 (0.04) when the total effective FWHM smoothing is 0.3 deg (1.0 deg). The asymmetry of the genus curve at the positive and negative threshold levels should not exceed |Delta g/g(nu=1,-1)| = 0.8% (4%) at 0.3 deg (1.0 deg) FWHM smoothing. Deviations of the observed MAP data in excess of these small values will be evidence for non-Gaussian behavior. The amplitude of the genus curve is a measure of the shape of the power spectrum at the smoothing scale. Even with the expected amount of instrumental noise and partial sky coverage (due to the Galaxy), the MAP data should allow discrimination amongst the cosmogonies considered at more than 99% confidence solely from a genus amplitude analysis.

astro-ph↗

arXiv1997

Evolution of Small Scale Cosmological Baryon Perturbations and Matter Transfer Functions

The evolution of small scale cosmological perturbations is carefully re-examined. Through the interaction with photons via electrons, baryon perturbations show interesting behavior in some physical scales. Characteristic features of the evolution of baryon density fluctuations are discussed. In CDM models, it is found a power-law growing phase of the small-scale baryon density fluctuations, which is characterized by the terminal velocity, after the diffusion (Silk) damping and before the decoupling epoch. Then, a transfer function for total matter density fluctuations is studied by taking into account those physical processes. An analytic transfer function is presented, which is applicable for the entire range up to a solar mass scale in the high$-z$ universe, and it is suitable also to the high baryon fraction models.

astro-ph↗

arXiv1997

Cosmological Baryon Sound Waves Coupled with the Primeval Radiation

The fluid equations for the baryon-electron system in an expanding universe are derived from the Boltzmann equation. The effect of the Compton interaction is taken into account properly in order to evaluate the photon-electron collisional term. As an application, the acoustic motions of the baryon-electron system after recombination are investigated. The effective adiabatic index $γ$ is computed for sound waves of various wavelengths, assuming the perturbation amplitude is small. The oscillations are found to be dumped when $γ$ changes from between 1 (for an isothermal process) to 5/3 (for an adiabatic process).

astro-ph↗

arXiv1997

MAX 4 and MAX 5 CMB anisotropy measurement constraints on open and flat-Lambda CDM cosmogonies

We account for experimental and observational uncertainties in likelihood analyses of cosmic microwave background (CMB) anisotropy data from the MAX 4 and MAX 5 experiments. These analyses use CMB anisotropy spectra predicted in open and spatially-flat Lambda cold dark matter cosmogonies. Amongst the models considered, the combined MAX data set is most consistent with the CMB anisotropy shape in Omega_0 ~ 0.1-0.2 open models and less so with that in old (t_0 >~ 15 - 16 Gyr, i.e., low h), high baryon density (Omega_B >~ 0.0175/h^2), low density (Omega_0 ~ 0.2 - 0.4), flat-Lambda models. The MAX data alone do not rule out any of the models we consider at the 2-sigma level. Model normalizations deduced from the combined MAX data are consistent with those drawn from the UCSB South Pole 1994 data, except for the flat bandpower model where MAX favours a higher normalization. The combined MAX data normalization for open models with Omega_0 ~ 0.1-0.2 is higher than the upper 2-sigma value of the DMR normalization. The combined MAX data normalization for old (low h), high baryon density, low-density flat-Lambda models is below the lower 2-sigma value of the DMR normalization. Open models with Omega_0 ~ 0.4-0.5 are not far from the shape most favoured by the MAX data, and for these models the MAX and DMR normalizations overlap. The MAX and DMR normalizations also overlap for Omega_0 = 1 and some higher h, lower Omega_B, low-density flat-Lambda models.

astro-ph↗

arXiv1997

Cosmology with x-matter

Motivated by the possibility of $H_0t_0 > 1$ where $H_0$ and $t_0$ are the Hubble parameter and the age of the universe, respectively, we investigate the cosmology including x-matter. x-matter is expressed by the equation of state $p_x=w_0ρ_{x0} + c_s^2(ρ_x-ρ_{x0})$, where $p_x$, $ρ_x$ and $ρ_{x0}$ are the pressure, the density of x-matter and the density at present, respectively. $w_0$ and $c_s^2$ are functions of $ρ_x$ in general. x-matter has the most general form of the equation of state which is characterized by 1)violation of strong energy condition at present for $w_0 < -1/3$ ; 2) locally stable (i.e. $c_s^2\geq 0$); 3)causality is guaranteed ($c_s\leq 1$). Considering the case that $w_0$ and $c_s^2$ are constants, we find that there is a large parameter space of $(w_0,c_s^2,Ω_{x0})$ in which the model universe is consistent with the age of the universe and the observations of distant Type I supernovae.

astro-ph↗

arXiv1997

Using SuZIE arcminute-scale CMB anisotropy data to probe open and flat-ΛCDM cosmogonies

We use arcminute-scale data from the Sunyaev-Zel'dovich Infrared Experiment to set limits on anisotropies in the cosmic microwave background radiation in open and spatially-flat-Lambda cold dark matter cosmogonies. There are no 2-sigma detections for the models tested. The upper limits obtained are consistent with the amplitude of anisotropy detected by the COBE/DMR experiment.

astro-ph↗