Kinetic, time irreversible evolution of the unstable $\pi^{\pm}$ - meson

In Liouville formalism the expression for density matrix, determining the time evolution of unstable $\pi^{\pm}$ - meson in the framework of unified formulation of quantum and kinetic dynamics is defined. The eigenvalues problem is investigated in the framework of Prigogine's principles of description of nonequilibrium processes at microscopic level. The problem was solved on the basis of complex spectral representation. It was shown that the approach leads to Pauli master equation for the weakly interacting system.