A SYSTEMATIC PROJECTION OPERATOR-FORMALISM IN NONEQUILIBRIUM STATISTICAL-MECHANICS

A systematic damping theoretical formalism is presented to give basic equations of statistical physics. Our formalism naturally yields the s o-called time convolution (TC) and time convolutionless (TCL) equation s both for a density matrix and for dynamical variables. The method is explicitly used to obtain equations in the Heisenberg picture (equati ons of motion for dynamical variables). In contrast to the existing de rivation of equations of motion, the present formalism gives a systema tic method for deriving these equations without specifying the project ion operator. Moreover, the formalism is valid even for time-dependent Hamiltonian systems. A simple example is given to illustrate our form alism.