The Symmetries of Fermion Fluids at Low Dimensions
  We point out that the quasiparticle spectrum of the Landau Fermi liquid theory has an extra $Z_2$ symmetry, local in momentum space, which is not generic to the Hamiltonian with interactions. Thus the Fermi liquid is in this sense a (quantum) zero-temperature critical point. 
Philip W. Anderson and F. Duncan M. Haldane