Fermion masses and mixings, flavor violation, and the Higgs boson mass in supersymmetric unified framework

Abstract

In spite of the impressive success of the standard model (SM) in explaining a wide variety of low energy experiments, many fundamental questions remain unanswered. Combining grand unification symmetry and flavor symmetry in the supersymmetric framework leads to interesting new physics that might solve many of the puzzles of the SM. I construct a supersymmetric grand unification model based on the gauge symmetry SO(10) and the non-abelian discrete symmetry A4. In the framework of this model the small mixings of the quark sector and the large mixings of the lepton sector are successfully accommodated by employing exotic heavy fermion fields with superheavy masses. An excellent fit to the quark and lepton masses and mixings as well as to the CP violation parameter is obtained. Flavor violating processes in the quark and lepton sectors within this realistic supersymmetric SO(10) x A4 model are also investigated. I find that flavor violation is induced at grand unification scale as a consequence of the large mixing of the light fermion fields and the exotic heavy fields. The stringent experimental constraint from u -> ey decay rate requires a high degree of degeneracy of the supersymmetry breaking soft scalar masses of the exotic heavy fields and supersymmetric scalar partners of the light fermion fields. The choice of slepton masses of order 1 TeV is found to be consistent with the constraints from branching ratio of u -> ey and with all other flavor changing neutral current (FCNC) processes being sufficiently suppressed.

In a related project, we study the effect of allowing messenger-matter mixing in a class of models with gauge-mediated supersymmetry breaking in the unification framework. We find that the maximal mixing condition that leads to the upper limit of the lightest Higgs mass (~ 125 GeV) of MSSM can be obtained in models with the messenger fields belonging to 10+10 representations of SU(5) gauge symmetry. Consistent with the cosmological preference for the messenger scale of < 3 x 10^8 GeV, the lightest Higgs mass of order 121 GeV is obtained, along with all superparticle masses below 1 TeV. Our results are also consistent with the gauge and exotic Yukawa couplings being perturbative and unified at the GUT scale as well as with all FCNC processes being suppressed in agreement with experimental bounds.