QUANTIZATION OF THE STRING INSPIRED DILATON GRAVITY AND THE BIRKHOFF THEOREM

We show that, for the pure dilaton CGHS model. the Gupta-Bleuler quant ization is viable because the constraints can be linearized due to pos itivity conditions present in the model (and not in the general string case). There is no ambiguity nor anomalies in the quantization. The e xpectation values of the metric and dilaton fields obey the classical requirements, thus exhibiting at the quantum level the Birkhoff theore m. (C) 1998 Published by Elsevier Science B.V.