Pinned branes and new non Lorentz invariant theories

We describe a mechanism for localising branes in ambient space. When a 3-fo rm flux is turned on in a Taub-NUT space, an M5-brane gets an effective pot ential that pins it to the center of the space. A similar effect occurs for M2-branes and D-branes with appropriate fluxes. In carefully chosen limits of the external parameters, this leads to new theories that are decoupled from gravity and appear to break Lorentz invariance. For example, we predic t the existence of a new 5 + 1D theory that breaks Lorentz invariance at hi gh-energy and has a low-energy description of N tensor multiplets with N = (1, 0) supersymmetry. We also predict a new type of theory that, similarly to the little-string theory decouples from gravity by a dynamical (rather t han kinematical) argument. (C) 2000 Elsevier Science B.V. All rights reserv ed.