Prof Subir Sarkar

Abstract:

The cosmological abundance of nucleons determined from considerations of Big Bang nucleosynthesis allegedly provides compelling evidence for non-nucleonic dark matter. Recent developments in measurements of primordial light element abundances, in particular deuterium and helium, require reexamination of this important issue. The present situation is uncertain but exciting.

Abstract:

In effective supergravity theories following from the superstring, a modulus field can quite naturally set the neccessary initial conditions for successful cosmological inflation to be driven by a hidden sector scalar field. The leading term in the scalar potential is {\em cubic} hence the spectrum of scalar density perturbations neccessarily deviates from scale-invariance, while the generation of gravitational waves is negligible. The growth of large-scale structure is then consistent with observational data assuming a critical density cold dark matter universe, with no need for a component of hot dark matter. The model can be tested thorough measurements of cosmic microwave background anisotropy on small angular scales.

Abstract:

We identify a new mechanism in supergravity theories which leads to successful inflation without any need for fine tuning. The simplest model yields a spectrum of density fluctuations tilted away from scale-invariance and negligible gravitational waves. We demonstrate that this is consistent with the observed large-scale structure for a cold dark matter dominated, critical density universe. The model can be tested through measurements of microwave background anisotropy on small angular scales.