Viable and testable SUSY GUTs with Yukawa unification: the case of split trilinears

Abstract

We explore general SUSY GUT models with exact third-generation Yukawa unification, but where the requirement of universal soft terms at the GUT scale is relaxed. We consider the scenario in which the breaking of universality inherits from the Yukawa couplings, i.e. is of minimal flavor violating (MFV) type. In particular, the MFV principle allows for a splitting between the up-type and the down-type soft trilinear couplings. We explore the viability of this trilinear splitting scenario by means of a fitting procedure to electroweak observables, quark masses as well as flavor-changing neutral current processes. Phenomenological viability singles out one main scenario. This scenario is characterized by a sizable splitting between the trilinear soft terms and a large mu term. Remarkably, this scenario does not invoke a partial decoupling of the sparticle spectrum, as in the case of universal soft terms, but instead it requires part of the spectrum, notably the lightest stop, the gluino and the lightest charginos and neutralinos to be very close to the current experimental limits. The above mechanism is mostly triggered by a non-trivial interplay between the requirements of negative, sizable SUSY threshold corrections to mb and an instead negligible modification of the B --> Xs gamma decay rate, in presence of various other constraints, most notably a successful EWSB and a not too large BR(Bs --> mu^_s16 mu^-). We present a model-building interpretation of our discussed scenario and emphasize the crucial role of SUSY spectrum determinations at the LHC for either falsifying Yukawa unification or else providing important hints on the mechanism of SUSY breaking at work.