Black hole entropy and the semiclassical approximation
  We compute the entropy of the Hawking radiation for an evaporating black hole, in 1+1 dimensions and in 3+1 dimensions. We investigate the validity of the semiclassical approximation for the evaporation process. It appears that there might be a large entropy of entanglement between the classical degrees of freedom describing the black hole and the radiation fields when the theory of quantum gravity plus matter is considered. 
Samir D. Mathur