Theory of a two-level system strongly interacting with a degenerate Fermi gas

A two-level system is treated which interacts with a degenerate fermionic heat bath. Arbitrarily strong screening by fermions is taken into account. The hopping of the two-level system may be spontaneous or assisted by the fermionic bath. By derivation of scaling equations it is shown for the spin-(1/2) case that because of the assisted hops the two-level system cannot be localized in one of the states.