Massive Dirac neutrinos and the SN1987A signal

We present results of calculations which incorporate the effect of massive Dirac neutrinos in numerical models for the cooling of the neutron star associated with SN1987A. In the Weinberg-Salam standard model, minimally extended to include Dirac neutrino masses, the production of sterile (positive helicity) neutrinos via neutral-current neutrino-nucleon scattering proceeds at a rate that significantly affects the energetics of cooling. We determine the expected number of events, total energy in neutrinos and the burst duration for both Kamiokande II and Irvine-Michigan-Brookhaven detectors. Due to an increase in the cooling rate caused by sterile neutrinos, we find that for m_νμ,τ= m_νμ²+m_ντ ²≥14 keV, the expected neutrino burst is shortened t o a duration that is inconsistent with the observations reported by both detectors. The calculations incorporate the feedback effects of the cooling due to sterile neutrinos in a self-consistent manner and the mass limit obtained is found to be largely insensitive to the equation of state used.