The dominance of type-II seesaw mechanism for neutrino masses has attracted considerable attention because of a number of advantages. We show a novel approach to achieve Type-II seesaw dominance in nonsupersymmetric SO(10) grand unification where a low mass 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∆ L 10 8 − 10 9 GeV, the model predicts new dominant contributions to neutrino-less double beta decay in the WL−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 ms 3.0 GeV, 2.0 GeV, and 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 flavor 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 proton lifetime for p → e + π 0 are found to be within the currently accessible search limits. Other aspects of model applications including leptogenesis etc. are briefly indicated.

We discuss gauge coupling unification of SU(3) C × SU(2) L × U(1) Y descending directly from non-supersymmetric SO(10) while providing solutions to the three outstanding problems of the standard model: neutrino masses, dark matter, and the baryon asymmetry of the universe. Conservation of matter parity as gauged discrete symmetry for the stability and identification of dark matter in the model calls for high-scale spontaneous symmetry breaking through 126 H Higgs representation. This naturally leads to the hybrid seesaw formula for neutrino masses mediated by heavy scalar triplet and right-handed neutrinos. Being quadratic in the Majorana coupling, the seesaw formula predicts two distinct patterns of right-handed neutrino masses, one hierarchical and another not so hierarchical (or compact), when fitted with the neutrino oscillation data. Predictions of the baryon asymmetry via leptogenesis are investigated through the decays of both the patterns of RHν masses. A complete flavor analysis has been carried out to compute CP-asymmetries including washouts and solutions to Boltzmann equations have been utilised to predict the baryon asymmetry. The additional contribution to vertex correction mediated by the heavy left-handed triplet scalar is noted to contribute as dominantly as other Feynman diagrams. We have found successful predictions of the baryon asymmetry for both the patterns of right-handed neutrino masses. The SU(2) L triplet fermionic dark matter at the TeV scale carrying even matter parity is naturally embedded into the non-standard fermionic representation 45 F of SO(10). In addition to the triplet scalar and the triplet fermion, the model needs a nonstandard color octet fermion of mass ∼ 5 × 10 7 GeV to achieve precision gauge coupling unification at the GUT mass scale M 0 U = 10 15.56 GeV.Open Access, c The Authors. Article funded by SCOAP 3 .doi:10.1007/JHEP04(2017)075 JHEP04(2017)075Threshold corrections due to superheavy components of 126 H and other representations are estimated and found to be substantial. It is noted that the proton life time predicted by the model is accessible to the ongoing and planned experiments over a wide range of parameter space.

In a recent review Mohapatra has discussed how type-I seesaw mechanism suppressed by fine tuning or specific textures of associated fermion mass matrices can form the basis of neutrino masses in TeV scale W R boson models. In this paper we review recent works in another class of theories where the added presence of gauge singlet fermions render the type-I seesaw contribution vanishing but extended seesaw dominant. In this case the light neutrino mass formula is the same as the classic inverse seesaw derived earlier but the singlet fermion masses are governed by a separate type-I seesaw like formula. Embeddings of this mechanism in supersymmetric as well as nonsupersymmetric SO(10) with low or intermediate masses of W R or Z R bosons are discussed. We also discuss how this cancellation criterion has led to a new mechanism of type-II seesaw dominance which permits U (1) B−L breaking scale much smaller than the left-handed triplet mass. Out of a number of new observable predictions, the most visible one in both cases are charged lepton flavor violating decays accessible to ongoing searches and dominant contribution to double beta decay mediated by the light gauge singlet fermions in the W L − W L channel. These seesaw dominance mechanisms are applicable in the extensions of the SM and high, intermediate, or low scale left-right gauge theories with or without their SO(10) origin. Recent applications of this mechanism covering dark matter and leptogenesis are reviewed. Emergence of other dominant seesaw mechanisms are also briefly pointed out.

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Inspired by various updated tantalizing results of LHCb on baryonic sector we study the [Formula: see text] decay in nonuniversal [Formula: see text] model. We present the fourfold angular distributions of the decay in terms of transversity amplitudes. We structure the observables: differential branching ratio, lepton side forward–backward asymmetries and polarization fractions in terms of the transversity amplitudes and incorporate the new physics (NP) terms in it. We reduce the number of the form factors using the improved Isgur–Wise relations. We study the observables in the Standard Model (SM) as well as in nonuniversal [Formula: see text] model. The predicted values are very interesting for the high energy physics community and results might provide prominent footprints of NP.