We discuss a realistic high scale (nu(B-L) approximately 10(12) GeV) supersymmetric seesaw model based on the gauge group SU(2)L x SU(2)R x SU(4)c where neutron-antineutron oscillation can be in the observable range. This is contrary to the naive dimensional arguments which say that tau(N-N) is proportional to nu(B-L)5 and should therefore be unobservable for seesaw scale nu(B-L) > or = 10(5) GeV. Two reasons for this enhancement are (i) accidental symmetries which keep some of the diquark Higgs masses at the weak scale and (ii) a new supersymmetric contribution from a lower dimensional operator. The net result is that tau(N-N) is proportional to nu(B-L)2 nu(wk)3 rather than nu(B-L)5. The model also can explain the origin of matter via the leptogenesis mechanism and predicts light diquark states which can be produced at LHC.
We show that in a class of minimal supersymmetric SO(10) models which have been found to be quite successful in predicting neutrino mixings, all proton decay modes can be suppressed by a particular choice of Yukawa textures. This suppression works for contributions from both left and right operators for nucleon decay and for arbitrary tan β. The required texture not only fits all lepton and quark masses as well as CKM parameters but it also predicts neutrino mixing parameter Ue3 and Dirac CP phase sin |δMNS | to be 0.07-0.09 and 0.3-0.7 respectively. We also discuss the relation between the GUT symmetry breaking parameters for the origin of these textures.
We consider the unification of gauge, Higgs as well as the matter fields in a 6D N = 2 supersymmetric SU(8) gauge theory. The gauge symmetry SU(8) is broken down to SU(4) × SU(2) L × SU(2) R × U(1) 2 in 4D through T 2 /Z 6 orbifold compactification, and the theory is reduced to 4D N = 1 supersymmetric Pati-Salam model. The electroweak Higgs fields as well as the third family of fermions are unified in the 6D N = 2 gauge multiplet. The 6D bulk gauge interaction provides both gauge and Yukawa interactions for the third family predicting α 1 = α 2 = α 3 = α t = α b = α τ at the unification scale, in good agreement with experiment. Incorporation of the first and second family as well as other orbifolds are also briefly discussed.
A minimal supersymmetric SO(10) model with one 10 and one 126 Higgs superfield has recently been shown to predict all neutrino mixings as well as the solar mass difference squared in agreement with observations. Two assumptions critical to the predictivity and success of the model are that: (i) the superpotential includes only renormalizable terms, thereby limiting the number of free parameters and (ii) the triplet term in the type II seesaw formula for neutrino mass dominates, leading to the sum rule M ν = c(M d − M e ) that is responsible for large mixings. However, CKM CP phase is constrained to be in the second or third quadrant requiring a significant non-CKM component to CP violation to explain observations. We revisit this issue using type I seesaw formula for neutrino masses and obtain the following results: (i) we show that the above sumrule responsible for large mixing angles can also emerge in type I seesaw models; the detailed predictions are however not compatible with present data for any choice of CP phases. (ii) We then show that addition of a nonrenormalizable term restores compatibility with neutrino data and CKM CP violation both in type I and type II cases. We further find that (iii) the MSSM parameter tan β ≥ 30 in the type I model and (iv) lepton flavor violation and lepton electric dipole moments which are accessible to proposed experiments in both type I and type II models. We also discuss the unification of the gauge couplings in type I model which requires an intermediate scale.
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