Description of a nuclear interaction in the Keldysh diagram technique and the problem of neutrino luminosity of neutron stars

The Keldysh diagram technique has been formulated for description of equilibrium and nonequilibrium nuclear systems. A nuclear interaction is constructed on the basis of the theory of finite Fermi systems. The formalism is applied to calculation of the probabilities of various processes. The possibilities of the proposed approach are demonstrated in calculation of the luminosity of the principal reactions which contribute to the cooling of neutron stars. The luminosity is calculated for the process nn→npenu-bar, which incurs in a dense nucleon medium very differently than in a rarefied medium. The dependence of the luminosity of the nucleon--nucleon correlation factor is analyzed. The formalism is applied to systems with pairing. The contribution to the luminosity of the reactions n/sub pa/→nνnu-bar and p/sub pa/→pνnu-bar, which are possible only in the presence of nucleon pairing, is calculated. The consequences of the results in the scenario of neutron-star cooling are discussed