Field Theoretic Approaches To Early Universe
  This thesis compiles the results of six works which deal with - inflationary model building and estimation of cosmological parameters from various field theoretic setup, quantification of reheating temperature, studies of leptogenesis in braneworld and estimation of primordial non-Gaussianity from ${\cal N}=1$ supergravity using $\delta N$ formalism. We start our discussion with exploring the possibility of MSSM inflation in the light of recent observed data from various D -flat directions using the saddle and inflection point techniques. The effective inflaton potential around saddle point and inflection point have been utilized in estimating the observable parameters and confronting them with WMAP7 and Planck dataset. Next we explore the possibility of inflation from the five dimensional ${\cal N} = 2$ supergravity setup by deriving the effective potential in the context of RS like braneworld model and DBI Galileon. After deriving an four dimensional effective potential, we obtain the inflationary observables from both the scenarios and confront them with the WMAP data. Further we fit the CMB angular power spectra from TT anisotropy and other polarization data obtained from WMAP. Further, we discuss the non-trivial features of reheating from supergravity inspired braneworld model, where the results are to some extent different from that of the usual low energy GR counterpart, because of the modified Friedmann equations in this setup. We explicitly derive the analytical expressions for the reheating temperature and further solve the evolution equation of the number density of thermal gravitino which results in the gravitino abundance. Finally, we study the primordial local type of non-Gaussian features using $\delta N$ formalism for a generic class of sub-Planckian models dominated by the Hubble-induced corrections within ${\cal N} = 1$ supergravity framework. 
Sayantan Choudhury
hep-th astro-ph.CO gr-qc hep-ph