Search

Nonsupersymmetric minimal SU(5) with Higgs representations 24H and 5H and standard fermions in 5¯F⊕10F is well known for its failure in unification of gauge couplings and lack of predicting neutrino masses. Like standard model, it is also affected by the instability of the Higgs scalar potential. We note that extending the Higgs sector by 75H and 15H not only leads to the popular type-II seesaw ansatz for neutrino masses with a lower bound on the triplet mass MΔ>2×109 GeV, but also achieves precision unification of gauge couplings without proliferation of nonstandard light Higgs scalars or fermions near the TeV scale. Consistent with recent LUX-2016 lower bound, the model easily accommodates a singlet scalar WIMP dark matter near the TeV scale which resolves the vacuum stability issue even after inclusion of heavy triplet threshold effect. We estimate proton lifetime predictions for p→e+π0 including uncertainties due to input parameters and threshold effects due to superheavy Higgs scalars and superheavy X±4/3,Y±1/3 gauge bosons. The predicted lifetime is noted to be verifiable at Super Kamiokande and Hyper Kamiokande experiments. [ABSTRACT FROM AUTHOR]

We evaluate the Majorana phases for a general 3 × 3 complex symmetric neutrino mass matrix on the basis of Mohapatra–Rodejohann's phase convention using the three rephasing invariant quantities I 12 , I 13 and I 23 proposed by Sarkar and Singh. We find them interesting as they allow us to evaluate each Majorana phase in a model independent way even if one eigenvalue is zero. Utilizing the solution of a general complex symmetric mass matrix for eigenvalues and mixing angles we determine the Majorana phases for both the hierarchies, normal and inverted, taking into account the constraints from neutrino oscillation global fit data as well as bound on the sum of the three light neutrino masses ( Σ i m i ) and the neutrinoless double beta decay ( β β 0 ν ) parameter | m 11 | . This methodology of finding the Majorana phases is applied thereafter in some predictive models for both the hierarchical cases (normal and inverted) to evaluate the corresponding Majorana phases and it is shown that all the sub cases presented in inverted hierarchy section can be realized in a model with texture zeros and scaling ansatz within the framework of inverse seesaw although one of the sub cases following the normal hierarchy is yet to be established. Except the case of quasi degenerate neutrinos, the methodology obtained in this work is able to evaluate the corresponding Majorana phases, given any model of neutrino masses. [ABSTRACT FROM AUTHOR]

We investigate scaling ansatz with texture zeros within the framework of linear seesaw mechanism. In this variant of seesaw mechanism a simplified expression of effective neutrino mass matrix m ν containing two Dirac type matrices ( m D and m DS ) and one Majorana type matrix ( m RS ) is obtained by virtue of neglecting the global U ( 1 ) L symmetry breaking term in the mass term of the Lagrangian. Along with the charged lepton mass matrix, the matrix m RS , too, is chosen in a diagonal basis whereas a scaling relation is incorporated in m D and m DS with different scale factors. Our goal in this work is to achieve a completely phenomenologically acceptable m ν generated by combinations of m D and m DS containing least number of independent parameters or maximum number of zeros. At the end of the numerical analysis it is found that number of zeros in any of the constituent Dirac type matrices ( m D and m DS ) of m ν cannot be greater than six in order to meet the phenomenological requirements. The hierarchy obtained here is normal and also the values of the two parameters sum mass ( ∑ m i ) and | m ν e e | are below the present experimental lower limit. [ABSTRACT FROM AUTHOR]

In a novel standard model extension it has been suggested that, even in the absence of right-handed neutrinos and type-I seesaw, purely triplet leptogenesis leading to baryon asymmetry of the universe can be realized by two heavy Higgs triplets which also provide type-II seesaw ansatz for neutrino masses. In this work we discuss this model predictions for hierarchical neutrino masses in concordance with recently determined cosmological bounds and oscillation data including θ 23 in the second octant and large Dirac CP phases. We find that for both normal and inverted orderings, the model fits the oscillation data with the sum of the three neutrino masses consistent with current cosmological bounds determined from Planck satellite data. In addition, using this model ansatz for CP-asymmetry and solutions of Boltzmann equations, we also show how successful predictions of baryon asymmetry emerges in the cases of both unflavoured and two-flavoured leptogeneses. With additional Z 2 discrete symmetry, a minimal extension of this model is further shown to predict a scalar singlet WIMP dark matter in agreement with direct and indirect observations which also resolves the issue of vacuum instability persisting in the original model. Although the combined constraints due to relic density and direct detection cross section allow this scalar singlet dark matter mass to be m ξ = 750 GeV, the additional vacuum stability constraint pushes this limiting value to m ξ = 1.3 TeV which is verifiable by ongoing experiments. We also discuss constraint on the model parameters for the radiative stability of the standard Higgs mass. [ABSTRACT FROM AUTHOR]