Dirac Quantization of Two-Dimensional Dilaton Gravity Minimally Coupled   to N Massless Scalar Fields
  It is shown that the Callan-Giddings-Harvey-Strominger theory on the cylinder can be consistently quantized (using Dirac's approach) without imposing any constraints on the sign of the gravitational coupling constant or the sign (or value) of the cosmological constant. The quantum constraints in terms of the original geometrical variables are also derived. 
Domingo Louis-Martinez (University of British Columbia)