Information Loss in Black Hole Evaporation
  Parikh-Wilczek tunnelling framework is investigated again. We argue that Parikh-Wilczek's treatment, which satisfies the first law of black hole thermodynamics and consists with an underlying unitary theory, is only suitable for a reversible process. Because of the negative heat capacity, an evaporating black hole is a highly unstable system. That is, the factual emission process is irreversible, the unitary theory will not be satisfied and the information loss is possible. 
Jingyi Zhang, Yapeng Hu, Zheng Zhao