 Low-energy Fermi-liquid quasiparticle lifetime

The Pauli exclusion principle restricts final states available to a low-energy Landau quasiparticle and the particle–hole pair it excites. In a regular three-dimensional Fermi liquid, this phase-space restriction makes the decay rate quadratic in excitation energy or temperature. The excitation's width divided by its energy therefore vanishes at the Fermi surface, allowing an asymptotically sharp quasiparticle despite interactions.