Speaker
Description
Neutrino oscillation measurements hint at non-zero neutrino masses, and the addition of gauge singlet right-handed neutrinos to the SM field content conveniently provides masses to the active neutrinos. A byproduct of this mechanism is the possible Majorana nature of neutrinos, which leads to lepton number violating effects, such as neutrinoless double beta decay. The standard study of these effects involves mass-dependent nuclear matrix elements which, although easy to use, might be missing important effects, especially in the light neutrino regime where the ultrasoft contributions become important. A fresh look at the different momentum regions leads us to an effective practical parametrisation for the decay amplitude that can show significant differences in the light-to-medium mass range of neutrinos compared to the standard parametrisation. The differences are compared for $^{136}$Xe and $^{76}$Ge, and as a concrete realisation of a UV model leading to Majorana neutrinos, the testability of a 3+2 model with two sterile neutrinos is discussed.
