AdS_2 and quantum stability in the CGHS model
  The two-dimensional anti-de Sitter space(AdS_2) is constructed in terms of the CGHS model. The geometric solutions are composed of the AdS vacuum and the AdS black hole which are locally equivalent but distinguishable by their mass. The infalling classical fields do not play any role but the quantum back reaction is crucial in the formation of the AdS vacuum and AdS black hole. In the presence of the AdS black hole, there does not exist any radiation, which is consistent with the constraint equations. Therefore the transition from the AdS black hole to the AdS vacuum is impossible, and they are quantum mechanically stable . We discuss the reason why the vanishing Hawking radiation appears in the AdS_2 black hole in contrast to asymptotically flat black holes. 
Won Tae Kim