A generalized photon propagator

Premetric electrodynamics is a useful formalism for unified description of a wide range of modified electrodynamics models. It is also applicable in describing of the electromagnetic processes in anisotropic media. In the current paper, we present a covariant gauge-independent derivation of the generalized dispersion relation for electromagnetic waves in a medium with a local, linear constitutive law. Moreover, we derive a generalized photon propagator (Green function in the momentum representation). For Maxwell constitutive tensor, the standard light cone structure and the standard Feynman propagator are reinstated. (fast track communication)