Gamma Rays and the Decay of Neutrinos from SN1987A

Abstract

We calculate limits to the properties of massive, unstable neutrinos using data from gamma-ray detectors on the Pioneer Venus Orbiter Satellite; a massive neutrino emitted from SN1987A that decayed in flight and produced gamma rays would be detectable by this instruments. The lack of such a signal allows us to constrain the branching ratio to photons ($\text{Bg}$), mass ($\text{mnu}$), and radiative lifetime (${\tau }_{\gamma }=\tau /\text{Bg}$). For low mass ($m<T\sim 8\text{MeV}$) neutrinos decaying $\nu \to {\nu }^{\prime }\gamma$, $\text{Bg}<3\times 10^{-7}$, for $\text{mt}\lesssim 10^6\text{keV}\sec$, and $\text{Bg}<6\times 10^{-14}\text{mt}/\text{keV}\sec$ for $\text{mt}\gtrsim 10^6\text{keV}\sec$; limits for high-mass neutrinos are somewhat weaker due to Boltzmann suppression. We also calculate limits for decays that produce gamma rays through the \brem channel, $\nu \to {\nu }^{\prime }{e}^{+}{e}^{-}\gamma$. In the case that neutrino mass states are nearly degenerate, $\delta m^2/m^2\ll 1$, our limits for the mode $\nu \to {\nu }^{\prime }\gamma$ become more stringent by a factor of $\delta m^2/m^2$, because more of the decay photons are shifted into the PVO detector energy window.

Comments: 17 pages, 6 postscript figures, uses revtex, epsf.sty. Submitted to PRD. Also available at file://ftp.cita.utoronto.ca/cita/jaffe/papers/pvoflux.ps.gz