Perturbations to theμ−τsymmetry, leptogenesis, and lepton flavor violation with the type II seesaw mechanism

Abstract

We study the possibility of generating non-zero reactor mixing angle θ 13 by perturbing the µ − τ symmetric neutrino mass matrix. The leading order µ − τ symmetric neutrino mass matrix originates from type I seesaw mechanism whereas the perturbations to µ − τ symmetry originate from type II seesaw term. We consider four different realizations of µ − τ symmetry: Bimaximal Mixing(BM), Tri-bimaximal Mixing (TBM), Hexagonal Mixing (HM) and Golden Ratio Mixing (GRM) all giving rise to θ 13 = 0, θ 23 = π 4 but different non-zero values of solar mixing angle θ 12 . We assume a minimal µ − τ symmetry breaking type II seesaw mass matrix as a perturbation and calculate the neutrino oscillation parameters as a function of type II seesaw strength. We then consider the origin of non-trivial leptonic CP phase in the charged lepton sector and calculate the lepton asymmetry arising from the lightest right handed neutrino decay by incorporating the presence of both type I and type II seesaw. We constrain the type II seesaw strength as well as leptonic CP phase (and hence the charged lepton sector) by comparing our results with experimental neutrino oscillation parameters as well as Planck bound on baryon to photon ratio.Finally, we extend our analysis on lepton flavour violating decays like µ → eγ and µ → eee due to exchange of TeV scale Higgs triplet scalar within the low scale type II seesaw framework. The branching ratios for these lepton flavour processes are examined with the small type II perturbation term ω and the estimated values are very close to the experimental bound coming from current search experiments.

Neutrinoless double beta decay in type I+II seesaw models

“…Such a combination of type I and type II seesaw together can also explain non-zero reactor mixing angle θ 13 as well as CP phases, as discussed in the works [48][49][50][51][52][53]. Making use of the presence of two equally dominating seesaw terms in the neutrino mass formula, we consider the possibility where either type I or type II or both type I and type II mass matrices can be arbitrary while structural cancellation [54] between them can give rise to the correct light neutrino mass matrix.…”

“…Making use of the presence of two equally dominating seesaw terms in the neutrino mass formula, we consider the possibility where either type I or type II or both type I and type II mass matrices can be arbitrary while structural cancellation [54] between them can give rise to the correct light neutrino mass matrix. Instead of considering completely arbitrary type I and type II mass matrices, we consider a specific type I seesaw mass matrix: tribimaximal (TBM) type which gives θ 13 = 0 [48][49][50][51][52][53]. The type II seesaw mass matrix is then…”

SpontaneousCPviolation in lepton-sector: A common origin forθ13, the DiracCPphase, and leptogenesis

“…This interplay is well studied in the literature [14][15][16][17][18][19][20][21][22][23]. In recent years keeping in mind that θ 13 is nonzero, efforts have been given to realize leptogenesis [24][25][26][27][28][29][30] and linking it with θ 13 in models based on type-II seesaw [31].…”

Connecting leptonic CP violation, lightest neutrino mass and baryon asymmetry through type II seesaw

“…In some of our recent works [31][32][33][34], we carried out an exercise of generating non-zero θ 13 by considering a model where both type I [35][36][37][38][39] and type II [40][41][42][43][44][45][46] seesaw are present.…”

“…This makes responsible for creating the lepton asymmetry. To calculate the baryon asymmetry, we follow the procedure adopted in our earlier works [33,34,52].…”