Derivation of Master Equations in the Presence of Initial Correlations with Reservoir: Projection Method Revisited

We discuss the derivation of master equations in the presence of initial correlations with the reservoir. In van Hove's limit, the total system behaves as if it started from a factorized initial condition. A proper choice of Nakajima-Zwanzig's projection operator is crucial and the reservoir should be endowed with the mixing property.