Stringy negative-tension branes and the second law of thermodynamics
  Negative energy objects generally lead to instabilities and a number of other disturbing behaviors. In particular, negative energy fluxes lead to a breakdown of the classical area theorem for black hole horizons, which can lead to violations of the second law of thermodynamics. The negative energy objects that arise in string theory involve special boundary conditions which remove the perturbative instabilities. We show that they have additional special features which allow them to evade contradiction with the second law. We identify one mechanism which applies for most orientifold planes in string theory, and distinct mechanisms for the O8-plane and the AdS soliton. 
Donald Marolf and Simon F. Ross