Particle creation in cosmological models with varying gravitational and cosmological "constants"

Einstein's field equations with variable gravitational coupling G = G(t) and decaying vacuum energy density Lambda = Lambda(t) are considered as describing matter creation in a cosmological framework. The particle creation rate is determined by the variation rate of both G and Lambda. By considering simple phenomenological evolution laws for G and Lambda, an exact solution of the gravitational field equations for a flat Friedmann-Robertson-Walker (FRW) space-time is obtained leading to a self-consistent cosmological model describing matter and entropy generation in the very early Universe.