Leptogenesis in supersymmetry with one L violating coupling

We have shown a new scenario of successful leptogenesis with one L violating coupling and a relative Majorana phase playing the role of CP violation. This is in contrast to the usual consideration of Feynman diagram with at least two L violating couplings. We have considered R-parity violating minimal supersymmetric standard model (MSSM) for leptogenesis at TeV scale. This scenario is also consistent with generating light neutrino mass if asymmetry is generated through semileptonic $$\lambda ^{\prime }$$ λ ′ coupling.

Quasi-Dirac neutrinos in the linear seesaw model

We implement a minimal linear seesaw model (LSM) for addressing the Quasi-Dirac (QD) behaviour of heavy neutrinos, focusing on the mass regime of MN ≲ MW. Here we show that for relatively low neutrino masses, covering the few GeV range, the same-sign to opposite-sign dilepton ratio, Rℓℓ, can be anywhere between 0 and 1, thus signaling a Quasi-Dirac regime. Particular values of Rℓℓ are controlled by the width of the QD neutrino and its mass splitting, the latter being equal to the light-neutrino mass mν in the LSM scenario. The current upper bound on mν1 together with the projected sensitivities of current and future |UN ℓ|2 experimental measurements, set stringent constraints on our low-scale QD mass regime. Some experimental prospects of testing the model by LHC displaced vertex searches are also discussed.

Radiative seesaw corrections and charged-lepton decays in a model with soft flavour violation

We consider the one-loop radiative corrections to the light-neutrino mass matrix and their consequences for the predicted branching ratios of the five lepton-flavour-violating decays $$ {\mathrm{\ell}}_1^{-}\to {\mathrm{\ell}}_2^{-}{\mathrm{\ell}}_3^{+}{\mathrm{\ell}}_3^{-} $$ ℓ 1 − → ℓ 2 − ℓ 3 + ℓ 3 − in a two-Higgs-doublet model furnished with the type-I seesaw mechanism and soft lepton-flavour violation. We find that the radiative corrections are very significant; they may alter the predicted branching ratios by several orders of magnitude and, in particular, they may help explain why BR (μ− → e−e+e−) is strongly suppressed relative to the branching ratios of the decays of the τ−. We conclude that, in any serious numerical assessment of the predictions of this model, it is absolutely necessary to take into account the one-loop radiative corrections to the light-neutrino mass matrix.

New Possibilities of Hybrid Texture of Neutrino Mass Matrix

We investigate the novel possibilities of hybrid textures comprising a vanishing minor (or element) and two equal elements (or cofactors) in light neutrino mass matrix Mν. Such type of texture structures leads to sixty phenomenological cases each, out of which only fifty-six are viable with texture containing a vanishing minor and an equality between the elements in Mν, while fifty are found to be viable with texture containing a vanishing element and an equality of cofactors in Mν under the current experimental test at 3σ confidence level. Detailed numerical analysis of all the possible cases has been presented.

Neutrino mass matrices from two zero 3 × 2 Yukawa textures and minimal d = 5 entries

Aiming to relate leptonic CP violating phase [Formula: see text] to the cosmological CP asymmetry, we study the extension of MSSM by two quasi-degenerate (strictly degenerate at tree level) right-handed neutrinos and consider all possible two texture zero [Formula: see text] Yukawa matrices plus one [Formula: see text] dimension five [Formula: see text] operator contributing to the light neutrino mass matrix. We classify all experimentally viable mass matrices, leading to several predictions, and analytically derive predictive relations. We also relate the CP violating [Formula: see text] phase to the CP phase of the thermal leptogenesis.

Leptogenesis in \(A_4\) Flavor Symmetry Model by Renormalization Group Evolution

We study how leptogenesis can be implemented in the seesaw models with \(A_4\) flavor symmetry, which lead to the tri-bimaximalneutrino mixing matrix. By considering renormalzation groupevolution from a high energy scale of flavor symmetry breaking(the GUT scale is assumed) to the low energy scale of relevantphenomena, the off-diagonal terms in a combination of DiracYukawa-coupling matrix can be generated. As aresult, the flavored leptogenesis is successfully realized. Wealso investigate how the effective light neutrino mass \(|\langle m_{ee}\rangle |\) associated with neutrinoless double beta decaycan be predicted byimposing the experimental data on the low energy observables. Wefind a link between the leptogenesis and the neutrinoless doublebeta decay characterized by \(|\langle m_{ee}\rangle|\) through ahigh energy CP phase $\phi$, which is correlated with the lowenergy Majorana CP phases. It is shown that the predictions of \(|\langle m_{ee}\rangle|\) for some fixed parameters of the highenergy physics can be constrained by the current observation ofbaryon asymmetry.

Neutrino Yukawa Textures within Type-I Seesaw

We review neutrino Yukawa textures with zeros within the framework of the type-I seesaw with three heavy right chiral neutrinos and in the basis where the latter and the charged leptons are mass diagonal. An assumed nonvanishing mass of every ultralight neutrino and the observed nondecoupling of any neutrino generation allow a maximum of four zeros in the Yukawa coupling matrix in family space. We show that the requirement of an exactμtsymmetry, coupled with the observational constraints, reduces seventy-two allowed such textures to only four corresponding to just two different forms of the light neutrino mass matrix: one with an inverted and the other with a normal mass ordering. The masses and Majorana phases of ultralight neutrinos are predicted within definite ranges with laboratory and cosmological observational inputs. Within the same framework, we also study Yukawa textures with a fewer number of zeros, but with exactμtsymmetry. We further formulate the detailed scheme of the explicit breaking ofμtsymmetry in terms of three small parameters for allowed four zero textures. The observed sizable mixing between the first and third generations of neutrinos is shown to follow for a suitable choice of these symmetry breaking parameters.