On Feynman's calculation of the Froehlich polaron mass

Feynman's formula for the effective mass of the Froehlich polaron is rederived from the formalism of projected partition functions. The mass is calculated as inverse of the diffusion coefficient of the polaron trajectory in imaginary time. It is shown that correlation between the electron and phonon boundary conditions in imaginary time is necessary for consistent derivation of the Feynman result.