Baryon asymmetry via leptogenesis in a neutrino mass model with complex scaling

Abstract

Baryogenesis via leptogenesis is investigated in a specific model of light neutrino masses and mixing angles. The latter was proposed on the basis of an assumed complex-extended scaling property of the neutrino Majorana mass matrix M ν , derived with a type-1 seesaw from a Dirac mass matrix m D and a heavy singlet neutrino Majorana mass matrix M R . One of its important features, highlighted here, is that there is a common source of the origin of a nonzero θ 13 and the CP violating lepton asymmetry through the imaginary part of m D . The model predicted CP violation to be maximal for the Dirac type and vanishing for the Majorana type. We assume strongly hierarchical mass eigenvalues for M R . The leptonic CP asymmetry parameter ε α 1 with lepton flavor α, originating from the decays of the lightest of the heavy neutrinos N 1 (of mass M 1 ) at a temperature T ∼ M 1 , is what matters here with the lepton asymmetries, originating from the decays of N 2,3 , being washed out. The light leptonic and heavy neutrino number densities (normalized to the entropy density) are evolved via Boltzmann equations down to electroweak temperatures to yield a baryon asymmetry through sphaleronic transitions. The effects of flavored vs. unflavored leptogenesis in the three mass regimes (1) M 1 < 10 9 GeV, (2) 10 9 GeV < M 1 < 10 12 GeV and (3) M 1 > 10 12 GeV are numerically worked out for both a normal and an inverted mass ordering of the light neutrinos. Corresponding results on the baryon asymmetry of the universe are obtained, displayed and discussed. For values close to the best-fit points of the input neutrino mass and mixing parameters, obtained from neutrino oscillation experiments, successful baryogenesis is achieved for the mass regime (2) and a normal mass ordering of the light neutrinos with a nonzero θ 13 playing a crucial role. However, the other possibility of an inverted mass ordering for the same mass regime, though disfavored, cannot be excluded. A discussion is also given on the sensitivity of our result to the masses M 2,3 of the heavier neutrinos N 2,3 .

Consequences of minimal seesaw with complex μτ antisymmetry of neutrinos

“…Existing references such as [42,72,73,93] also discuss leptogenesis within the framework of residual CP symmetry (in particular CP µτ ) and point out the nonoccurrence of unflavored leptogenesis and only the viability of the τ −flavored scenario similar to our proposal of a exact µτ antisymmetry in the neutrino sector. However, the final numerical analysis is different from our case.…”

“…This mechanism makes use of two heavy right chiral neutrino fields N Ri (i = 1, 2) with a Majorana mass matrix M R . We work in a basis in which M R is real, positive and diagonal [72,73]…”

“…For a hierarchical RH mass spectrum, refs. [72,73] shows a variation of Y B with a single model parameter for a fixed value of M 1 and best-fit values of the oscillation parameters. However, here we focus on the bounds on M 1 for the entire parameter space as well as the for the parameter set that corresponds to the observables which lie near to their best-fit values.…”

“…Since in our chosen basis [72,73], RH neutrinos are nondegenerate, it would also be interesting to study leptogenesis with a mildly hierarchical including a quasidegenerate N R mass spectrum. We will see later in this discussion that RH neutrinos which are not strongly hierarchical might obliterate all the new bounds on M 1 that we obtained earlier.…”

Generalized ℤ2 × ℤ2 in scaling neutrino Majorana mass matrix and baryogenesis via flavored leptogenesis

“…Since M R is taken to be diagonal i.e., M R = diag (M 1 , M 2 , M 3 ), the corresponding symmetry generator matrix G R is diagonal [65,66] with entries ±1, i.e.,…”