arXiv subjects

Naoshi Sugiyama

Publications and source records attributed to Naoshi Sugiyama.

149 records · Page 9Linked to original sources

arXiv1994

Microwave Background Fluctuations in an Open Universe

( to appear in: Proceedings of the Nishonomiya Yukawa Memorial Symposium Edited by M. Sasaki) There are several models for generating fluctuations in an open universe that are compatible with the microwave background fluctuations detected by COBE {\it and} observations of large scale structure. Topological defects, such as strings and textures, appear to be more successful in a low-$Ω$ model than in an $Ω= 1$ model. These models predict that the cosmic microwave background (CMB) fluctuations are non-Gaussian with distinctive signatures that may lead to their confirmation. If there exists a mechanism for generating scale invariant mass fluctuations, $(δM/M)^2 \propto M^{-4/3}$, then these models are also compatible with COBE. Both models predict mass fluctuations on the 8/h Mpc scale, $σ_8$, $\sim 0.5 - 1$ for $Ωh \sim 0.2 - 0.3$. A variety of observations of large-scale structure, clusters and galaxies, as well as the age problem, suggest that the low-$Ω$ models are attractive.

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arXiv1994

Small-Scale Cosmic Microwave Background Anisotropies as a Probe of the Geometry of the Universe

We perform detailed calculations of cosmic microwave background (CMB) anisotropies in a CDM-dominated open universe with primordial adiabatic density perturbations for a variety of reionization histories. We show that to a great extent, the CMB anisotropies depend only on the geometry of the Universe, which in a matter dominated universe is determined by $Ω$, and the optical depth to the surface of last scattering. In particular, the location of the primary Doppler peak depends primarily on $Ω$ and is fairly insensitive to the other unknown parameters, such as $Ω_b$, $h$, $Λ$, and the shape of the power spectrum. Therefore, measurements of CMB anisotropies on small scales may be used to determine $Ω$.

astro-ph↗

arXiv1993

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 $n - Ω_b$ plane in the case of $λ_0=1-Ω_b$ (flat models) and $λ_0=0$ (open models), where $n$ is the primordial spectral index of entropy fluctuations and $Ω_b$ 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.

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arXiv1993

Reionization and Cosmic Microwave Anisotropies

The effects of reionization, occurring after standard recombination in cold dark matter-dominated models, on CMB anisotropies are investigated. Late-time reionization reduces the CMB anisotropies, in particular, on degree scales. It is found that constraints on cold dark matter-dominated models from the highest frequency channel of the 9-point South Pole data are significantly relaxed for models which are consistent with Big Bang nucleosynthesis if reionization is assumed to have occurred by redshift $\sim 20.$

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arXiv1993

The Small Scale Integrated Sachs-Wolfe Effect

The integrated Sachs-Wolfe effect (ISW) can be an important factor in the generation of Cosmic Microwave Background anisotropies on all scales, especially in a reionized curvature or lambda dominated universe. We present an analytic treatment of the ISW effect, which is analogous to thick last scattering surface techniques for the Doppler effect, that compares quite well with the full numerical calculations. The power spectrum of temperature fluctuations due to the small scale ISW effect has wave number dependence k^{-5} times that of the matter power spectrum.

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