Phase diffusion in stationary state of nonequilibrium Bose gas
  Properties of low energy spectrum of elementary excitations in nonequilibrium Bose gas in stationary state with the dynamical equilibrium of outgoing and incoming of particles are studied. It is shown that due to the noise effect, typical for nonequilibrium systems, this spectrum has a diffusion character, in contradiction with the thermodynamically equilibrium systems, where this spectrum has a sound form. 
V. S. Babichenko
cond-mat.quant-gas cond-mat.soft