Comment on "Consistent thermostatistics forbids negative absolute   temperatures"
  In this comment we argue that negative absolute temperatures are a well-established concept for systems with bounded spectra. They are not only consistent with thermodynamics, but are even unavoidable for a consistent description of the thermal equilibrium of inverted populations. 
Ulrich Schneider, Stephan Mandt, Akos Rapp, Simon Braun, Hendrik   Weimer, Immanuel Bloch, Achim Rosch
cond-mat.quant-gas cond-mat.stat-mech quant-ph