Cosmic Background Anisotropies in CDM Cosmology

Cosmic microwave background (CMB) anisotropies and density fluctuations are calculated for flat cold dark matter (CDM) models with a wide range of parameters, i.e., $\Omega_0, h$ and $\Omega_B$ for both standard recombination and various epochs of reionization. Tables of the power spectrum of CMB anisotropies in the form of $C_\ell$'s as a function of $\ell$ are presented. Although the Harrison-Zeldovich initial spectrum is assumed in these tables, we present simple approximations for obtaining the $C_\ell$'s corresponding to a tilted spectrum from those with a Harrison-Zeldovich spectrum. The $\sigma_8$ values are obtained for the matter density spectrum, with $\sigma(10^\circ)$, fixed $Q_{rms-PS}$ and COBE DMR 2 year normalizations. Simple modifications of the fitting formula of the density transfer function which are applicable for models with high baryon density are given. By using both numerical results and these fitting formulae, we calculate the relation between $\sigma_8$ and $Q_{rms-PS}$, and find good agreement. Velocity fields are also calculated.Comment: 30 pages including 10 figures, uuencoded comressed Postscript. 3 figures are missing. A complete version is available at anonymous ftp site ftp://pac2.berkeley.edu/pub/sugiyama/sugiyama.uu Tables (39pages) are also available at ftp://pac2.berkeley.edu/pub/sugiyama/tables.ps (and tables.tex) Replaced because one new figure is added and some figures are modifie

Small Scale Cosmological Perturbations: An Analytic Approach

Through analytic techniques verified by numerical calculations, we establish general relations between the matter and cosmic microwave background (CMB) power spectra and their dependence on cosmological parameters on small scales. Fluctuations in the CMB, baryons, cold dark matter (CDM), and neutrinos receive a boost at horizon crossing. Baryon drag on the photons causes alternating acoustic peak heights in the CMB and is uncovered in its bare form under the photon diffusion scale. Decoupling of the photons at last scattering and of the baryons at the end of the Compton drag epoch, freezes the diffusion-damped acoustic oscillations into the CMB and matter power spectra at different scales. We determine the dependence of the respective acoustic amplitudes and damping lengths on fundamental cosmological parameters. The baryonic oscillations, enhanced by the velocity overshoot effect, compete with CDM fluctuations in the present matter power spectrum. We present new exact analytic solutions for the cold dark matter fluctuations in the presence of a growth- inhibiting radiation {\it and} baryon background. Combined with the acoustic contributions and baryonic infall into CDM potential wells, this provides a highly accurate analytic form of the small-scale transfer function in the general case.Comment: Revised accepted version; no changed results but several minor typos corrected; index & other roadmaps added. TeX + 20 Fig

Probing large scale filaments with HI and 3^3HeII

We explore the observability of the neutral hydrogen (HI) and the singly-ionized isotope helium-3 ($^3$HeII) in the intergalactic medium (IGM) from the Epoch of Reionization down to the local Universe. The hyperfine transition of $^3$HeII, which is not as well known as the HI transition, has energy splitting corresponding to 8 cm. It also has a larger spontaneous decay rate than that of neutral hydrogen, whereas its primordial abundance is much smaller. Although both species are mostly ionized in the IGM, the balance between ionization and recombination in moderately high density regions renders them abundant enough to be observed. We estimate the emission signal of both hyperfine transitions from large scale filamentary structures and discuss the prospects for observing them with current and future radio telescopes. We conclude that HI in filaments is possibly observable even with current telescopes after 100 hours of observation. On the other hand, $^3$HeII is only detectable with future telescopes, such as SKA, after the same amount of time.Comment: 21 pages, 13 figures, 2 tables, accepted to MNRA

Possibility of Ultra High-Energy Cosmic Rays from the Giant Flare in SGR 1806-20

On 2004 December 27, a giant flare from the soft gamma repeater 1806$-$20 was observed. The radiation mechanism of the initial peak of the flare would be controversial. In this letter we point out that very high-energy cosmic rays would be produced in the case that the flare was caused by internal shocks, as is usually considered for gamma-ray bursts. The highest energy of cosmic rays can reach $10^{19}$ eV, if the Lorentz factor of the shocks is sufficiently high. Future observations of cosmic rays will inform us about the mechanism of the giant flare.Comment: 8 pages, 2figure

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.Comment: 29 pages, LaTex, Submitted to Astrophysical Journa

Microwave Background Anisotropies in Primeval Isocurvature Baryon Models: Constraints on the Cosmological Parameters

We have performed the most comprehensive predictions of the temperature fluctuations \dtt in the primeval isocurvature baryon models to see whether or not the models are consistent with the recent data on the cosmic microwave background anisotropies. More specifically, we computed the \dtt corresponding to the experimental set-up by the South-Pole and the Owens Valley experiments as well as the COBE satellite. The amplitudes of the predicted \dtt are normalized by means of the COBE 10$^\circ$ data. The resulting constraints on the models are presented on $n - \Omega_b$ plane in the case of $\lambda_0=1-\Omega_b$ (flat models) and $\lambda_0=0$ (open models), where $n$ is the primordial spectral index of entropy fluctuations and $\Omega_b$ is the present baryon density parameter. Our results imply that the PIB models cannot be reconciled with the current observations for any reasonable set of cosmological parameters.Comment: 10pages and 4figures compressed uuencoded postscript (with figures), UTAP-93-16