Theory of the Unusual Quasiparticle Excitations in USb$_2$

A band of long-lived quasiparticles with a renormalized dispersion relation that does not cross the Fermi surface has been observed in USb$_2$ by angle resolved photoemission measurements. The existence of a kink in the quasiparticle dispersion relation of a band that does not cross the Fermi energy is unprecedented. We show that the observed renormalization does not come from the standard theory of electron-phonon renormalizations. We consider the effect of the interband self-energy and vertex corrections as possible causes for the formation of the renormalized quasiparticles. The effect of temperature is also considered.