Improved GUT and SUSY breaking by the same field

Abstract

In a previous paper, we presented a model in which the {\em same} modulus field breaks SUSY and a simple GUT gauge group, and which has {\em dynamical} origins for {\em both} SUSY breaking and GUT scales. In this model, the supergravity (SUGRA) and gauge mediated (GM) contributions to MSSM scalar and gaugino masses are comparable - this enables a realistic spectrum to be attained since GM contribution to the right-handed (RH) slepton (mass)^2 by itself (i.e., neglecting SUGRA contribution to sfermion {\em and} gaugino masses) is negative. But, in general, the SUGRA contribution to sfermion masses (from non-renormalizable contact Kähler terms) leads to flavor violation. In this paper, we use the recently proposed idea of gaugino mediated SUSY breaking (\tilde{g}MSB) to improve the above model. With MSSM matter and SUSY breaking fields localized on separate branes in an extra dimension of size R \sim 5 M^{-1}_{Pl} (in which gauge fields propagate), the SUGRA contribution to sfermion masses (which violates flavor) is suppressed. As in 4 dimensions, MSSM gauginos acquire {\em non}-universal masses from both SUGRA and GM - gaugino masses (in particular the SUGRA contribution to gaugino masses), in turn, generate acceptable sfermion masses through RG evolution; the phenomenology is discussed briefly. We also point out that a) in models where SUSY is broken by a GUT non-singlet field, there is, in general, a contribution to MSSM gaugino (and scalar) masses from the coupling to heavy gauge multiplet which {\em might} be {\em comparable} to the SUGRA contribution and b) models of GM proposed earlier which also have negative RH slepton (mass)^2 can be rendered viable using the \tilde{g}MSB idea.