Constraints on CDM cosmology from galaxy power spectrum, CMB and SNIa evolution

We examine the constraints that can be obtained on standard cold dark matter models from the most currently used data set: CMB anisotropies, type Ia supernovae and the SDSS luminous red galaxies. We also examine how these constraints are widened when the equation of state parameter $w$ and the curvature parameter $\Omega_k$ are left as free parameters. For the $\Lambda$CDM model, our 'vanilla' model, cosmological parameters are tightly constrained and consistent with current estimates from various methods. When the dark energy parameter $w$ is free we find that the constraints remain mostly unchanged, i.e. changes are smaller than the 1 sigma uncertainties. Similarly, relaxing the assumption of a flat universe leads to nearly identical constraints on the dark energy density parameter of the universe $\Omega_\Lambda$, baryon density of the universe $\Omega_b$, the optical depth $\tau$, the index of the power spectrum of primordial fluctuations $n_S$, with most one sigma uncertainties better than 5%. More significant changes appear on other parameters: while preferred values are almost unchanged, uncertainties for the physical dark matter density $\Omega_ch^2$, Hubble constant $H_0$ and $\sigma_8$ are typically twice as large. We found that different methodological approaches on large scale structure estimates lead to appreciable differences in preferred values and uncertainty widths. We also found that possible evolution in SNIa intrinsic luminosity does not alter these constraints by much, except for $w$, for which the uncertainty is twice as large. At the same time, this possible evolution is severely constrained. We conclude that systematic uncertainties for some estimated quantities are similar or larger than statistical ones.Comment: Revised version, 9 pages, 8 figures, accepted for publication in A&

Some FRW Models of Accelerating Universe with Dark Energy

The paper deals with a spatially homogeneous and isotropic FRW space-time filled with perfect fluid and dark energy components. The two sources are assumed to interact minimally, and therefore their energy momentum tensors are conserved separately. A special law of variation for the Hubble parameter proposed by Berman (1983) has been utilized to solve the field equations. The Berman's law yields two explicit forms of the scale factor governing the FRW space-time and constant values of deceleration parameter. The role of dark energy with variable equation of state parameter has been studied in detail in the evolution of FRW universe. It has been found that dark energy dominates the universe at the present epoch, which is consistent with the observations. The physical behavior of the universe is discussed in detail.Comment: 10 pages, 5 figure

Thermodynamics of phantom energy in the presence of a Reissner-Nordstrom black hole

In this paper, we study the validity of the generalized second law (GSL) in phantom dominated universe in the presence of a Reissner-Nordstr\"{o}m (RN) black hole. Our study is independent of the origin of the phantom like behavior of the considered universe. We also discuss the GSL in the neighborhood of transition from quintessence to phantom regime. We show that for a constant equation of state parameter, the GSL may be satisfied provided that the temperature is proportional to de Sitter temperature. It is shown that in models with (only) a transition from quintessence to phantom regime the generalized second law does not hold in the transition epoch. Next we show that if the phantom energy has a chemical potential, then the GSL will hold if the mass of black hole is above from a critical value.Comment: 5 pages, Accepted for publication in Astrophysics & Space Scienc

Inhomogeneous Bulk Viscous Fluid Universe with Electromagnetic Field and Variable Λ\Lambda-Term

Cylindrically symmetric inhomogeneous cosmological model for bulk viscous fluid distribution with electromagnetic field is obtained. The source of the magnetic field is due to an electric current produced along the z-axis. $F_{12}$ is the non-vanishing component of electromagnetic field tensor. To get the deterministic solution, it has been assumed that the expansion $\theta$ in the model is proportional to the shear $\sigma$. The values of cosmological constant for these models are found to be small and positive at late time, which are consistent with the results from recent supernovae Ia observations. Physical and geometric aspects of the models are also discussed in presence and absence of magnetic field.Comment: 21 pages, 8 figure

Gender shock: practising feminism on two continents/ Eisentein

vi, 138 hal.; 21 cm

Contemporary feminist thought/ Eisentein

xx, 196 hal.; 19 cm