Nonlinear Sachs-Wolfe effect in the early universe

Abstract

We investigate the influence of nonlinear metric perturbation to anisotropy of temperature in the early universe, considering the second order density perturbations in a spatially flat Friedmann-Robertson-Walker background. The Sachs-Wolfe effect, temperature anisotropy caused by photons traveling in the perturbed metic, is calculated by solving the geodesic equation of propagating light. In this thesis, we calculate the Sachs-Wolfe effect up to second order by choosing the longitudinal gauge. Also, we use the gradient expansion method in order to deal with the superhorizon mode.