The role of Causality in Tunable Fermi Gas Condensates
  We develop a new formalism for the description of the condensates of cold Fermi atoms whose speed of sound can be tuned with the aid of a narrow Feshbach resonance. We use this to look for spontaneous phonon creation that mimics spontaneous particle creation in curved space-time in Friedmann-Robertson-Walker and other model universes. 
Jen-Tsung Hsiang, Chi-Yong Lin, Da-Shin Lee, and Ray J. Rivers
gr-qc cond-mat.quant-gas