arXiv subjects

T. R. Seshadri

Publications and source records attributed to T. R. Seshadri.

40 records · Page 3Linked to original sources

arXiv2001

Cosmic Microwave Background Polarization Signals from Tangled Magnetic Fields

Tangled, primordial cosmic magnetic fields create small rotational velocity perturbations on the last scattering surface (LSS) of the cosmic microwave background radiation (CMBR). For fields which redshift to a present value of $B_0 = 3\times 10^{-9}$ Gauss, these vector modes are shown to generate polarization anisotropies of order $0.1μK - 4 μK$ on small angular scales ($ 500 < l < 2000$), assuming delta function or a power law spectra with $n=-1$. About 200 times larger signals result for $n=2$ spectra. Unlike inflation generated, scalar modes, these signals are dominated by the odd parity, B-type polarization, which could help in their detection.

astro-ph↗

arXiv2001

Quintessential Inflation with Dissipative fluid

We have investigated cosmological models with a self-interacting scalar field and a dissipative matter fluid as the sources of matter. Different variables are expressed in terms of a {\it generating function}. Exact solutions are obtained for one particular choice of the {\it generating function} The potential corresponding to this generating function is a standard tree-level potential arising in the perturbative regime in quantum field theory. With suitable choice of parameters, the scale factor in our model exhibits both inflationary behaviour in the early universe as well as an accelerating phase at late times with a decelerating period in between. It also satisfies the constraints for primeval nucleosynthesis and structure formation and seems to solve the cosmic coincidence problem. The solution exhibits a attractor nature towards a asymptotic de-sitter universe.

gr-qc↗

arXiv1999

Nature of Clustering in the Las Campanas Redshift Survey

We have carried out a multi-fractal analysis of the distribution of galaxies in the three Northern slices of the Las Campanas Redshift Survey. Our method takes into account the selection effects and the complicated geometry of the survey. In this analysis we have studied the scaling properties of the distribution of galaxies on length scales from $20 h^{-1} Mpc$ to $200 h^{-1} Mpc$. Our main results are: (1) The distribution of galaxies exhibits a multi-fractal scaling behaviour over the scales $20 h^{-1} Mpc$ to $80 h^{-1} Mpc$, and, (2) the distribution is homogeneous on the scales $80h^{-1} Mpc$ to $200 h^{-1} Mpc$. We conclude that the universe is homogeneous at large scales and the transition to homogeneity occurs somewhere in the range $80 h^{-1} Mpc$ to $100 h^{-1} Mpc$.

astro-ph↗

arXiv1998

A Vishniac type contribution to the polarisation of the CMBR?

Radiation which has a quadrupole component of anisotropy, can get polarized by Thomson scattering from charged particles. In the cosmological context, the microwave background photons develop significant quadrupole anisotropy as they free stream away from the the epoch of standard recombination. Reionization in the post recombination era can provide free electrons to Thomson scatter the incident anisotropic $CMBR$ photons. We compute the resulting polarisation anisotropy on small (arc-minute) angular scales. We look for significant non-linear contributions, as in the case of Vishniac effect in temperature anisotropy, due to the coupling of small-scale electron density fluctuations, at the new last scattering surface, and the temperature quadrupole. We show that, while, in cold dark matter type models, this does not lead to very significant signals ($\sim 0.02 - 0.04 μK$), a larger small angular scale polarization anisotropy, ($\sim 0.1 - 0.5μK$), can result in isocurvature type models.

astro-ph↗