Constraints on neutrino mixing with a 17-keV neutrino

We examine the constraints on the neutrino mass matrix consistent with the recent rediscovery of a 17-keV neutrino, the absence of neutrinoless double-β decay, and neutrino oscillation experiments. There are two cases consistent with the data, assuming only three Majorana neutrinos. One possibility is that the muon neutrino is heavier than 190 keV, and there is a lower bound on the probability ${\mathit{P}}_{\mathrm{\mu }\mathit{e}}$ of a muon neutrino oscillating into an electron neutrino, ${\mathit{P}}_{\mathrm{\mu }\mathit{e}}$>1.3×${10}^{\mathrm{-}3}$. The other possibility is that the muon neutrino is degenerate with the 17-keV neutrino to within an accuracy of ${10}^{\mathrm{-}11}$. In either case, there is a lower limit on the ${\nu }_{\mathit{e}}$ disappearance probability, ${\mathit{P}}_{\mathit{e}\to \mathit{e}}$≳0.02.