New mechanism for Type-II seesaw dominance in SO(10) with low-mass Z′,RH neutrinos, and verifiable LFV, LNV and proton decay

Abstract

The dominance of Type-II seesaw mechanism for the neutrino masses has attracted considerable attention because of a number of advantages. We show a novel approach to achieve Type-II seesaw dominance in non-supersymmetric SO(10) grand unification where a low-mass $$Z^{\prime }$$Z′boson and specific patterns of right-handed neutrino masses are predicted within the accessible energy range of the Large Hadron Collider. In spite of the high value of the seesaw scale, $$M_{\Delta _L} \simeq 10^8$$MΔL≃108–$$10^9$$109 GeV, the model predicts new dominant contributions to neutrino-less double beta decay in the $$W_L$$WL–$$W_L$$WL channel close to the current experimental limits via exchanges of heavier singlet fermions used as essential ingredients of this model even when the light active neutrino masses are normally hierarchical or invertedly hierarchical. We obtain upper bounds on the lightest sterile neutrino mass $$m_s\lesssim 3.0$$ms≲3.0 GeV, $$2.0$$2.0 GeV and $$0.7$$0.7 GeV for normally hierarchical, invertedly hierarchical and quasi-degenerate patterns of light-neutrino masses, respectively. The underlying non-unitarity effects lead to lepton flavour violating decay branching ratios within the reach of ongoing or planned experiments and the leptonic CP-violation parameter nearly two order larger than the quark sector. Some of the predicted values on the proton lifetime for $$p\rightarrow e^+\pi ^0$$p→e+π0are found to be within the currently accessible search limits. Other aspects of model applications including leptogenesis etc. are briefly indicated.