Viable quark-lepton Yukawa ratios and nucleon decay predictions in $SU(5)$ GUTs with type-II seesaw

Abstract

We investigate the viability of predictive schemes for quark-lepton Yukawa ratios and nucleon decay in non-supersymmetric SU(5) Grand Unified Theories (GUTs) where neutrino masses are generated by a type II seesaw mechanism. The scalar sector of the considered scenario contains 5-, 24-and 45-dimensional representations plus a 15dimensional representation for realising the type II seesaw. Predictions for the ratios of the quark and lepton Yukawa couplings emerge when the relevant entries of the Yukawa matrices are generated from single joint GUT operators (i.e. under the condition of single operator dominance). Focusing on the 2nd and 3rd family and hierarchical Yukawa matrices, we show that only two sets of predictions, yτ y b = 3 2 , yµ ys = 9 2 and yτ y b = 2, yµ ys = 6 are viable. To further investigate both options, we extend the minimal scenarios to two "toy models", including the 1st family of charged fermions, and calculate the models' predictions, e.g. for the nucleon decay rates and for the masses of the light relics that are potentially within reach of colliders.

Viable quark-lepton Yukawa ratios and nucleon decay predictions in SU(5) GUTs with type-II seesaw

“…With these higher dimensional operators at hand, models similar to the GJ model can be build if the following two conditions are satisfied: (i) the Yukawa matrices should be hierarchical, (ii) the 22-and 33-entry should be dominated by a single GUT operator, a concept which is referred to as single operator dominance [28][29][30]. 1 Following this approach, non-SUSY GUT scenarios in which neutrino masses are generated by a type I or a type II seesaw have been investigated in [27], respectively [45]. For GUT scenarios with a type I seesaw it was shown that the GUT scale ratios y τ /y b = 3/2 and y µ /y s = 9/2 are compatible with the experimental data.…”