All Or Nothing: On the Small Fluctuations of Two-Dimensional   String-Theoretic Black Holes
  A comprehensive analysis of small fluctuations about two-dimensional string-theoretic and string-inspired black holes is presented. It is shown with specific examples that two-dimensional black holes behave in a radically different way from all known black holes in four dimensions. For both the $SL(2,R)/U(1)$ black hole and the two-dimensional black hole coupled to a massive dilaton with constant field strength, it is shown that there are a {\it continuous infinity} of solutions to the linearized equations of motion, which are such that it is impossible to ascertain the classical linear response. It is further shown that the two-dimensional black hole coupled to a massive, linear dilaton admits {\it no small fluctuations at all}. We discuss possible implications of our results for the Callan-Giddings-Harvey-Strominger black hole. 
Gerald Gilbert and Eric Raiten