On the mass of a two dimensional quantum black hole

Abstract For the two dimensional dilaton-coupled quantum gravity model, we give the local hole mass, which is an analogue of what was first introduced by Fischler, Morgan and Polchinski in the four dimensional gravitational systems. We analyze the original CGHS model with this local mass and find that the local mass stays constant at past null infinity while on the matter shock wave line it gradually increases and diverges at the singularity. However it tends to decrease towards future null infinity.