Massive higher dimensional gauge fields as messengers of supersymmetry breaking

We consider theories with one or more compact dimensions with size r > 1/M,where M is the fundamental Planck scale, with the visible and hidden sectorslocalized on spatially separated "3-branes." We show that a bulk U(1) gaugefield spontaneously broken on the hidden-sector 3-brane is an attractivecandidate for the messenger of supersymmetry breaking. In this scenario scalarmass-squared terms are proportional to U(1) charges, and therefore naturallyconserve flavor. Arbitrary flavor violation at the Planck scale gives rise toexponentially suppressed flavor violation at low energies. Gaugino masses canbe generated if the standard gauge fields propagate in the bulk; \mu and B\muterms can be generated by the Giudice-Masiero or by the VEV of a singlet in thevisible sector. The latter case naturally solves the SUSY CP problem. Realisticphenomenology can be obtained either if all microscopic parameters are orderone in units of M, or if the theory is strongly coupled at the scale M. (Forthe latter case, we estimate parameters by extending "naive dimensionalanalysis" to higher-dimension theories with branes.) In either case, the onlyunexplained hierarchy is the "large" size of the extra dimensions infundamental units, which need only be an order of magnitude. All soft massesare naturally within an order of magnitude of m_{3/2}, and trilinear scalarcouplings are negligible. Squark and slepton masses can naturally unify even inthe absence of grand unification.Comment: Messenger gauge symmetry must be broken in hidden sector to avoid FCNC's; main conclusions unchanged. 25 pages, LaTeX2e, 2 eps figure