Is Nothing Sacred? Vacuum Energy, Supersymmetry and Lorentz Breaking   from Recoiling D branes
  Classical 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. 
John Ellis (CERN), N.E. Mavromatos (Kings College London), D.V.   Nanopoulos (TAMU, HARC, Academy of Athens)