Extra Dimensions String theory is an attempt to describe the universe in terms of 1-dimensional extended objects in a 10- (or 11-) dimensional universe. In order to avoid discrepancies with the observed 3+1 dimensional universe in which we live, string theorists must compactify 6 (or 7) of the dimensions. The size of the compact dimensions is generally assumed to be very small, of order the Planck Length of 10-35 m (corresponds to 1/MP where MP is the Planck mass of 1019 GeV). Arkani-Hamed, Dimopoulos and Dvali noted that the extra dimensions were not constrained by experiment to be very small and could in fact be nearly mm scale corresponding to much smaller mass scales (~TeV) and possibly leading to observable effects in collider experiments. Professor Raman Sundrum and his colleague Lisa Randall developed the idea of extra dimensions in an exciting new direction by separating two 4-D hypersurfaces (branes) by a small extra (5th) dimension. In their original model, our universe lives on one brane, the TeV brane with negative energy density and there exists a second, Planck brane of positive energy density separated by the extra dimension. The energy density of the branes warps the space-time in the 5-D bulk. This causes gravity which is a weak force corresponding to a high mass scale on the TeV brane to become a strong force corresponding to a low mass scale on the Planck brane. This effectively solves the hierarchy problem and predicts that there should be exotic TeV-scale spin 2 states (Kaluza-Klein or KK gravitions) produced in high energy accelerators. Professor Sundrum continues to study RS models and Professor Bagger studies supersymmetric variants of theories with extra dimensions. The LHC experiments should be sensitive to TeV scale states associated with these theories. An analysis of the sensitivity of a seach for RS KK gravitions in CMS by Collard and Lemaire is shown at the right. Next Page