Experimental Constraints on Seesaw Parameters in the Wigner-like Parametrization

Abstract

By introducing three right-handed neutrino singlets, the popular canonical seesaw mechanism is able to simultaneously explain the tiny masses of Majorana neutrinos and the baryon asymmetry of the Universe. In this paper, we provide an explicit calculation in this model with the help of the Wigner-like parametrization. We work in a special ansatz where both ${\mathbf{m}}_{\mathrm{D}}^{†}{\mathbf{m}}_{\mathrm{D}}^{}$ and ${\mathbf{m}}_{\mathrm{R}}^{†}{\mathbf{m}}_{\mathrm{R}}^{}$ are diagonal, with ${\mathbf{m}}_{\mathrm{D}}^{}$ and ${\mathbf{m}}_{\mathrm{R}}^{}$ being accordingly the Dirac and Majorana neutrino mass matrices, and $[{\mathbf{m}}_{\mathrm{D}}^{†}{\mathbf{m}}_{\mathrm{D}}^{},{\mathbf{m}}_{\mathrm{R}}^{†}{\mathbf{m}}_{\mathrm{R}}^{}]=0$ holds. Physical observables can be exactly calculated without any approximation, where three light Majorana neutrino masses $m_i^{}$, leptonic mixing angles ${\theta }_{ij}^{}$, CP-violating phases $\{\delta ,\rho ,\sigma \}$, and three rotation angles ${\vartheta }_i^{}$ describing the hierarchy between electroweak and seesaw scales are chosen as input parameters. For demonstration, we evaluate the branching fractions of the lepton-flavor-violating decays of charged leptons and the CP-violating asymmetries in the resonant thermal leptogenesis. The model parameters are constrained by the latest experimental limits.

18 pages, 4 figures, more discussions and references added, version accepted by PLB

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