Discriminating neutrino mass models using type-II see-saw formula

Abstract

In this paper we propose a kind of natural selection which can discriminate the three possible neutrino mass models, namely the degenerate, inverted hierarchical and normal hierachical models, using the framework of Type II seesaw formula. We arrive at a conclusion that the inverted hierarchical model appears to be most favourable whereas the normal hierarchical model follows next to it. The degenerate model is found to be most unfavourable. The neutrino mass matrices which are obtained using the usual canonical seesaw formula (Type I), and which also give almost good predictions of neutrino masses and mixings consistent with the latest neutrino oscillation data, are re-examined in the light of non-canonical seesaw formula (Type II). We then estimate a parameter γ which represents the minimum degree of suppression of the extra term arising from the left-handed Higgs triplet, so as to restore the good predictions on neutrino masses and mixings already had in Type I seesaw model.

Type-II seesaw mass models and baryon asymmetry

“…Following the predictions of SO(10) grand unified theory, we estimate the baryon asymmetry for two choices of Dirac neutrino mass matrix: case(i) Dirac neutrino mass matrix taken as charged lepton mass matrix and case(ii) Dirac neutrino mass matrix taken as up quark mass matrix. For specific values of the discriminator 'γ' extracted from type-II seesaw formula [2], we observe that the baryon asymmetry is dominated by type-I term only.…”

“…With this motivation different neutrino mass models [1,2] were constructed on the basis of celebrated seesaw mechanism [3]. All the models were checked for masses, mixings and stability under radiative corrections.…”

“…The second term denoted by m The solar and atmospheric neutrino oscillation experiments usually measure only the mass-square differences and in general we have three possible patterns of neutrino masses [13]: (a) Degenerate m 1 ≃ m 2 ≃ m 3 , (b) Inverted hierarchical m 1 ≃ m 2 >> m 3 and (c) Normal hierarchical m 1 << m 2 << m 3 . Depending upon the relative CP-phase of (m 1 , m 2 ) pair, the degenerate and inverted hierarchical models are further classified as: degenerate type-1A (DegT1A), degenerate type-1B (DegT1B), degenerate type-1C (DegT1C), inverted hierarchical Type-2A (InvT2A) and inverted hierarchical Type-2B (InvT2B), and these zeroth-order left-handed Majorana mass matrices [2,13] are collected in Appendix A for ready reference. The present forms [1,2] of various mass models given in Appendix B, are derived from seesaw mechanism(1).…”

“…Without fine tuning, we generally have γ ∼ 1, but we are searching the input values of γ where the contribution of second term arising from the presence of left-handed Higgs triplets is just sufficient to restore the good predictions of m I LL already acquired [2] in type-I seesaw framework. If the second term is dominant, the relevant good predictions of m I LL are spoiled.…”

“…As a representative example, we consider normal hierarchical mass model and the corresponding heavy right-handed neutrino mass matrix and light lefthanded neutrino mass matrices are [1,2] collected from Appendix B:…”