Neutrino Mass Matrices with $M_{ee} = 0$

Understand

Motivated by the possibility that the amplitude for neutrinoless double beta decay may be much smaller than the planned sensitivity of future experiments, we study ansatze for the neutrino mass matrix with $M_{ee} = 0$.

• For the case in which CP is conserved, we consider two classes of real-valued mass matrices: "Class I" defined by $|M_{e\mu}| = |M_{e\tau}|$, and "Class II" defined by $|M_{\mu\mu}| = |M_{\tau\tau}|$.
• The important phenomenological distinction between the two is that Class I permits only "small" values of $V_{e3}$ up to $\sim 0.03$, while Class II admits "large" values of $V_{e3}$ up to its empirical upper limit of 0.22.
• Then we introduce CP-violating complex phases into the mass matrix.