Limit on Γ(π0→νanti ν) from SN1987A

We consider the possible neutrino emission from SN1987A generated through the process γγ→π0→νanti ν, which is permitted when the neutrinos have a right-handed component. This energy-loss mechanism is consistent with the supernova neutrino observations if the decay rate Γ(π0→νanti ν)<(0.15-6.3)x10-13 eV. When the reaction π0→νanti ν is mediated by weak gauge bosons the limit on the decay rate allows us to obtain constraints on neutrino masses, mν<5-27 keV, depending on the core temperature. (orig.)