Discrete-time construction of nonequilibrium path integrals on the Kostantinov–Perel’ time contour

摘要: Rigorous nonequilibrium actions for the many-body problem are usually derived by means of path integrals combined with a discrete temporal mesh on Schwinger-Keldysh time contour. The latter suffers from fundamental limitation: initial state this contour cannot be arbitrary, but necessarily needs to described non-interacting density matrix, while interactions switched adiabatically. Kostantinov-Perel' overcomes these and other limitations, allowing generic initial-state preparations. In Article, we apply technique rigorously build integral