Improved GUT and SUSY breaking by the same field

In a previous paper [1], we presented a model in which the same modulus field breaks SUSY and a simple GUT gauge group (down to the SM gauge group). In this model, the supergravity (SUGRA) and gauge mediated contributions to MSSM scalar and gaugino masses are comparable – this enables a realistic spectrum to be attained since the gauge mediated contribution to the right-handed (RH) slepton (mass) (at the weak scale) by itself (i.e., neglecting SUGRA contribution to sfermion 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 (g̃MSB) to improve the above model. With MSSM matter and SUSY breaking fields localized on separate branes in an extra dimension of size R ∼ 5M P l (in which gauge fields proagate), the SUGRA contribution to sfermion masses (which violates flavor) is suppressed. As in 4 dimensions, MSSM gauginos acquire nonuniversal masses from both SUGRA and gauge mediation – gaugino masses (in particular the SUGRA contribution to gaugino masses), in turn, generate acceptable sfermion masses through renormalization group (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 heavy gauge multiplet which might be comparable to the SUGRA contribution and b) models of gauge mediation proposed earlier which also have negative RH slepton (mass) can be rendered viable using the g̃MSB idea. PACS numbers: 12.60.Jv, 14.80.Ly, 12.10.Dm This work is supported by DOE Grant DE-FG03-96ER40969. email: [email protected]