arXiv subjects

A. A. Starobinsky

Publications and source records attributed to A. A. Starobinsky.

75 records · Page 5Linked to original sources

arXiv1994

Confrontation of Double-Inflationary Models with Observations

We consider double-inflationary models with two noninteracting scalar fields, a light scalar field $ϕ_l$ with potential $\frac{1}{2}m_l^2ϕ_l^2$ and a heavy scalar field $ϕ_h$ with potential $\fracλ{n}ϕ_h^n$ with $n=2,4$. CDM with the initial spectrum of adiabatic perturbations produced in these models is compared with observations. These models contain two more free parameters than the standard CDM model with an initial scale-invariant spectrum. We normalize our spectra to COBE DMR and compare the predictions with observations on the biasing factor, large-scale peculiar velocities, quasar and galaxy formation and the Stromlo-APM counts-in-cells analysis. The model with $n=4$ is excluded by the data while for the $n=2$ model, taking cosmic variance into account, a small window of parameters compatible with observations is found.

astro-ph↗

arXiv1993

Non-Linear Approximations to Gravitational Instability: A Comparison in Second-Order Perturbation Theory

Nonlinear approximation methods such as the Zeldovich approximation, and more recently the frozen flow and linear potential approximations, are sometimes used to simulate nonlinear gravitational instability in the expanding Universe. We investigate the relative accuracy of these approximations by comparing them with the exact solution using second order perturbation theory. We evaluate the density and velocity fields in these approximations to second order, and also determine the skewness parameter $S_3 = \langle δ^3 \rangle / \langle (δ^{(1)})^2\rangle ^2$ for each of the approximations again in second order. We find that $S_3 = 4, ~3, ~3.4$ for the Zeldovich approximation, the frozen flow and the linear potential approximations respectively as compared to $S_3 = {34/7}$ for the exact solution. Our results show that, of all the approximations considered, the Zeldovich approximation is the most accurate in describing the weakly nonlinear effects of gravity. Moreover, the Zeldovich approximation is much closer to the exact results for matter and velocity distributions than the other approximations if the slope of the power spectrum of density perturbations is $-3< n \le -1$.

astro-ph↗

arXiv1993

New Restrictions on Spatial Topology of the Universe from Microwave Background Temperature Fluctuations

If the Universe has the topology of a 3-torus ($T^3$), then it follows from recent data on large-scale temperature fluctuations $ΔT/T$ of the cosmic microwave background that either the minimal size of the torus is at least of the order of the present cosmological horizon, or the large-scale $ΔT/T$ pattern should have a symmetry plane (in case of the effective $T^1$ topology) or a symmetry axis (in case of the effective $T^2$ topology), the latter possibility being probably excluded by the data.

gr-qc↗