Renormalization of nonequilibrium dynamics in FRW cosmology

We derive the renormalized nonequilibrium equations of motion for a scalar field and its quantum back reaction in a conformally flat Friedmann-Robertson-Walker universe. We use a fully covariant formalism proposed by us recently for handling numerically and analytically nonequilibrium dynamics in the one-loop approximation. The system is assumed to be in a conformal vacuum state initially. We use dimensional regularization; we find that the counterterms can be chosen independent of the initial conditions though the divergent leading order graphs do depend on them. {copyright} {ital 1997} {ital The American Physical Society}