2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/33548Classical superstring vacua have zero vacuum energy and are supersymmetric and Lorentz-invariant. We argue that all these properties may be destroyed when quantum aspects of the interactions between particles and non-perturbative vacuum fluctuations are considered. A toy calculation of string/D-brane interactions using a world-sheet approach indicates that quantum recoil effects - reflecting the gravitational back-reaction on space-time foam due to the propagation of energetic particles - induce non-zero vacuum energy that is linked to supersymmetry breaking and breaks Lorentz invariance. This model of space-time foam also suggests the appearance of microscopic event horizons.28 pages LaTeX, 5 eps figures, talk presented by DVN at 4th International Symposium On Sources And Detection Of Dark Matter In The Universe (DM 2000), Marina del Rey, California, 20-23 Feb 2000General Relativity and Quantum CosmologyAstrophysicsHigh Energy Physics - PhenomenologyHigh Energy Physics - Theorytext