New Supernova Constraints on Sterile-Neutrino Production.

We consider the possibility that a light sterile-neutrino species \nu_S can be produced by \nu_e scattering during the cooling of a proto-neutron star. If we parameterize the sterile neutrino production cross-section by a parameter A as \sigma (\nu_e X\rightarrow \nu_S X) = A \sigma(\nu_e X\rightarrow \nu_e X), where X is an electron, neutron or proton, we show that A is constrained by limits to the conversion of \nu_e to \nu_S in the region between the sterile-neutrino trapping region and the electron-neutrino trapping region. This consideration excludes values of A in the range between 10^{-4} \la A \la 10^{-1}.