Small extra dimensions from the interplay of gauge and supersymmetry breaking

Higher-dimensional theories provide a promising framework for unified extensions of the supersymmetric Standard Model. Compactifications to four dimensions often lead to U(1) symmetries beyond the Standard Model gauge group, whose breaking scale is classically undetermined. Without supersymmetry breaking, this is also the case for the size of the compact dimensions. Fayet-Iliopoulos terms generically fix the scale M of gauge symmetry breaking. The interplay with supersymmetry breaking can then stabilize the compact dimensions at a size 1/M, much smaller than the inverse supersymmetry breaking scale 1/mu. We illustrate this mechanism with an SO(10) model in six dimensions. compactified on an orbifold. (C) 2008 Elsevier B.V. All rights reserved.