Exact parametrization of a minimal seesaw model

Abstract

We propose a parametrization of neutrino masses and mixing in the minimal seesaw model (MSM). The MSM, which introduces two heavy sterile neutrinos, is the minimal extension of the Standard Model in addressing the tiny masses of active neutrinos. The parametrization includes 11 free parameters: 6 neutrino oscillation parameters (2 mass-squared differences $\Delta m^2_{21}$, $\Delta m^2_{31}$, 3 mixing angles $\theta_{12}$, $\theta_{13}$, $\theta_{23}$, and 1 Dirac phase $\delta_{\rm CP}$), 1 mass parameter in $0\nu2\beta$ decay $m_{ee}$, and 4 additional parameters: 2 heavy neutrino masses $M_1$ and $M_2$, 1 active-sterile mixing angle $\theta_{14}$ and 1 CP-violating phase $\delta_{14}$. This parametrization is derived exactly from the most general neutrino mass matrix in the MSM without any approximation. We further discuss its implications in phenomenological studies.