Light Majorana Neutrinos in (Semi)invisible Meson Decays

Understand

We reconsider decays of pseudoscalar mesons (P) to neutrino pairs and possibly additional photons in presence of (light) Majorana neutrinos.

• For this purpose we derive a model-independent general parametrization of neutrino mass matrices with physically interpretable and irreducible set of parameters.
• The parametrization is valid for any number of neutrinos and interpolates smoothly between the heavy Majorana and the (pseudo)Dirac neutrino limits.
• We apply the new parametrization to the study of $P \rightarrow \nu \nu$ and $P \rightarrow \nu \nu \gamma$ decays within the SM extended by additional singlet fermions.