Cerenkov radiation by neutrinos in a supernova core

Neutrinos with a magnetic dipole moment propagating in a medium with a velocity larger than the phase velocity of light emit photons by the Cerenkov process. The Cerenkov radiation is a helicity flip process via which a left-handed neutrino in a supernova core may change into a sterile right-handed one and free stream out of the core. Assuming that the luminosity of such sterile right handed neutrinos is less than 10(53) ergs/sec gives an upper bound on the neutrino magnetic dipole moment mu(nu) < 0.3 x 10(-13)mu(beta). This is 2 orders of magnitude more stringent than the previously established bounds on mu(nu) from considerations of supernova cooling rate by right-handed neutrinos.