Nucleon Decay in Non-Minimal Supersymmetric SO(10)

Evaluation of nucleon decay modes and branching ratios in a non-minimal supersymmetric SO(10) grand unified theory is presented. The non-minimal GUT considered is the supersymmetrised version of the ‘realistic’ SO(10) model originally proposed by Harvey, Reiss, and Ramond, which is realistic in that it gives acceptable charged fermion and neutrino masses within the context of a phenomenological fit to the low energy standard model inputs. Despite a complicated Higgs sector, the SO(10) 10 Higgs superfield mass insertion is found to be the sole contribution to the tree level F-term governing nucleon decay. The resulting dimension 5 operators that mediate nucleon decay give branching ratio predictions parameterised by a single parameter, the ratio of the Yukawa couplings of the 10 to the fermion generations. For parameter values corresponding to a lack of dominance of the third family self coupling, the dominant nucleon decay modes are p → K+ + ν̄μ and n → K0 + ν̄μ, as expected. Further, the charged muon decay modes are enhanced by two orders of magnitude over the standard minimal SUSY SU(5) predictions, thus predicting a distinct spectrum of ‘visible’ modes. These charged muon decay modes, along with p → π+ + ν̄μ and n → π0 + ν̄μ, which are moderately enhanced over the SUSY SU(5) prediction, suggest a distinguishing fingerprint of this particular GUT model, and if nucleon decay is observed at Super-KAMIOKANDE the predicted branching ratio spectrum can be used to determine the validity of this ‘realistic’ SO(10) SUSY GUT model.