On the dispute between Boltzmann and Gibbs entropy
  Very recently, the validity of the concept of negative temperature has been challenged by several authors since they consider Boltzmann's entropy (that allows negative temperatures) inconsistent from a mathematical and statistical point of view, whereas they consider Gibbs' entropy (that does not admit negative temperatures) the correct definition for microcanonical entropy.   In the present paper we prove that for systems with equivalence of the statistical ensembles Boltzmann entropy is the correct microcanonical entropy. Analytical results on two systems supporting negative temperatures, confirm the scenario we propose. In addition, we corroborate our proof by numeric simulations on an explicit lattice system showing that negative temperature equilibrium states are accessible and obey standard statistical mechanics prevision. 
Pierfrancesco Buonsante, Roberto Franzosi and Augusto Smerzi (QSTAR   and CNR - Istituto Nazionale di Ottica)
cond-mat.stat-mech