State of a conduction electron in a crystal in the case of nonlocal interaction with elementary excitations

It is shown by means of the electron-exciton interaction that conduction electrons may interact nonlocally with uncharged elementary excitations in a crystal. In the case of such an interaction the carrier state is very different from the polaron state. The carrier energy spectrum is investigated for the case of a nonlocal electron-exciton interaction at $T=0$ for weak and strong electron-exciton coupling. Upper and lower bounds for the ground-state energy of such a quasiparticle (transferon) are found for an arbitrary electron-exciton coupling.