Zero sound, spin fluctuations, and effective mass in liquid He3

The coupling of density and spin-density fluctuations to the single-particle excitations in He3 at zero temperature is studied. The present results exhibit a sharply peaked effective mass close to the Fermi surface, caused by the attractive quasiparticle interaction in the spin-1 particle-hole channel. The coupling to the zero-sound mode causes a secondary maximum around 2kF. This mechanism can reconcile the rapid variation of the specific heat with a well-defined zero-sound mode at large momenta.