Unitary evolution of perturbations of a two-dimensional black hole

We discuss massive scalar perturbations of a two-dimensional dilaton black hole. We employ a Pauli-Villars regularization scheme to calculate the effect of the scalar perturbation on the Bekenstein-Hawking entropy. By concentrating on the dynamics of the scalar field near the horizon, we argue that quantum effects alter the effective potential. We calculate the two-point function explicitly and show that it exhibits Poincaré recurrences.