Thermodynamic nonextensivity in a closed string gas
  Well known results in string thermodynamics show that there is always a negative specific heat phase in the microcanonical description of a gas of closed free strings whenever there are no winding modes present. We will carefully compute the number of strings in the gas to show how this negative specific heat is related to the fact that the system does not have thermodynamic extensivity. We will also discuss the consequences for a system of having a microcanonical negative specific heat versus the exact result that such a thing cannot happen in any canonical (fixed temperature) description. 
Manuel A. Cobas, M. A. R. Osorio, Mar\'ia Su\'arez (University of   Oviedo, Asturias, Spain)