Bounds on the neutrino magnetic moment from SN 1987 A

We examine the emission of wrong helicity neutrinos from SN 1987 A due to neutrino magnetic moment (μv). We consider the case when the core of nascent neutron star is on the verge of pion condensation. The relevant processes are the p + π− → n + νl,rνl,r and πνl (νr) → πνr (νl). We have also studied the case where the core is assumed to have undergone a phase transition to quark matter. The important process here is q + νl (νr) → q + νr (νl). By imposing a bound on νr luminosity, we get a limit on μv≲(0.3−0.05)×10−12 μb depending on the temperature and composition of the core.