Gravity and Lorentz Breakdown in Higher-Dimensional Theories and Strings

Abstract

The gravitational phenomenology of theories compactified from higher di- mensions is investigated. Emphasis is placed on the consequences in string theory of tensor-induced spontaneous breaking of the higher-dimensional Lorentz symmetry. The role played by this mechanism in causing a gravi- tational version of the Higgs effect and in compactification is studied. The phenomenology of compactified theories with massless modes is compared with experiment via an examination of non-leading but observable grav- itational effects arising in the presence of a localized matter distribution. Further constraints from known cosmological features of the universe are presented. The results significantly constrain many theories involving ext.ra dimensions in their perturbative regime. A mechanism is needed that leaves massless the physical spacetime components of the higher-dimensional met- ric while generating masses for other components. Some suggestions for overcoming this metric-mass problem are made.