### HMC Physics Colloquium

*Tuesdays at 16:30 in Shanahan Center for Teaching and Learning, Room B460*

## Tom Banks

University of California at Santa Cruz

String Theory and Holography: An Approach to the Quantum Theory of Gravity

Jan. 23, 2007

String theory provides us with a number of examples of well defined quantum theories of gravitation in asymptotically flat and asymptotically Anti de Sitter (maximally symmetric space with negative cosmological constant) space-times. For low space-time curvature, these theories have an exact symmetry between bosonic and fermionic particles (supersymmetry) which is not shared by the real world. The problem of relating string theory to the real world has to do with understanding how to construct a theory where this symmetry is broken, and how the size of the breaking of this symmetry is related to the (positive) cosmological constant that is indicated by various astrophysical observations (or if there is such a relation). I will sketch two alternative speculative approaches to this problem.