RENORMALIZATION AND BOLTZMANN EQUATIONS IN THERMAL QUANTUM-FIELD THEORY

The renormalization scheme in nonequilibrium thermal quantum field the ories is reexamined. Instead of the self-energy diagonalization scheme , we propose to diagonalize Green's function at equal time. This elimi nates the problem of on-shell definition related to time-dependent ene rgies and spatially inhomogeneous situations, and yields a Boltzmann e quation that contains memory effect. The new diagonalization scheme an d the derivation of the Boltzmann equation from it can be applied to a ny thermal situation. It allows the treatment of a nonequilibrium prob lem beyond perturbational calculations in a self-consistent manner. Th e results are applicable to both thermo field dynamics and the closed time path formalism.