Constraining the (low-energy) type-I seesaw Lagrangian

Abstract

The type-I seesaw Lagrangian yields a nongeneric set of active-sterile oscillation parameters---the neutrino mass eigenvalues and the physical elements of the full mixing matrix are entwined. For this reason one is able to, in principle, test the model by performing enough measurements which are sensitive to neutrino masses and lepton mixing. We point out that for light enough right-handed neutrino masses---less than 10 eV---next-generation short-baseline neutrino oscillation experiments may be able to unambiguously rule out (or ``rule in'') the low-energy seesaw as the Lagrangian that describes neutrino masses. These types of searches are already under consideration in order to address the many anomalies from accelerator neutrino experiments (LSND, MiniBooNe), reactor neutrino experiments (the ``reactor anomaly''), and others. In order to test the low-energy seesaw, it is crucial to explore different oscillation channels, including ${\ensuremath{\nu}}_{e}$ and ${\ensuremath{\nu}}_{\ensuremath{\mu}}$ disappearance and ${\ensuremath{\nu}}_{\ensuremath{\mu}}\ensuremath{\leftrightarrow}{\ensuremath{\nu}}_{\ensuremath{\tau}}$ appearance.