ar X iv : 0 70 5 . 24 30 v 1 [ he p - th ] 1 6 M ay 2 00 7 Poincaré recurrences of Schwarzschild black holes ∗

We discuss massive scalar perturbations of a Schwarzschild black hole. We argue that quantum effects alter the effective potential near the horizon resulting in Poincaré recurrences in Green functions. Results at the semi-classical level are independent of the details of the modification of the potential provided its minimum near the horizon is inversely proportional to the square of the Poincaré time. This modification may be viewed as a change in the near-horizon geometry. We consider explicitly the examples of a brick wall, a smooth cutoff and a wormhole-like modification showing that they all lead to the same results at leading order.