Choptuik scaling and quantum effects in 2D dilaton gravity

We study numerically the collapse of massless scalar fields in two-dimensional dilaton gravity, both classically and semiclassically. At the classical level, we find that the black hole mass scales at threshold like M(BH)proportional to\p-p*\(gamma), where gamma similar or equal to 0.53. At the semiclassical level, we find that in general M-BH approaches a nonzero constant as p->p*. Thus, one-loop effects suggest a mass gap not present classically at the onset of black hole formation.