On the energy-momentum spectrum of a homogeneous Fermi gas
  We consider translation invariant quantum systems in thermodynamic limit. We argue that their energy-momentum spectra should have shapes consistent with effective models involving quasiparticles. Our main example is second quantized homogeneous interacting Fermi gas in a large cubic box with periodic boundary conditions, at zero temperature. We expect that its energy-momentum spectrum has a positive energy gap and a positive critical velocity. 
Jan Derezi\'nski, Krzysztof A. Meissner and Marcin Napi\'orkowski
math-ph math.MP