Functional variational approach to polaron models

A general approach to the investigation of polaron systems using path integrals is presented. The basis of the approach is a functional variational method which generalizes Feynman's to the case of a nonvanishing momentum of the system. The characteristics of a free polaron and the behavior of a polaron system in the presence of weak external perturbations are investigated. Questions associated with polaron thermodynamics are considered. The high-temperature behavior of the mean energy and the polaron mass are studied, as is the reaction of a polaron system at finite temperatures to an external perturbation