{hacek C}erenkov 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 {hacek C}erenkov process. The {hacek C}erenkov 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{sup 53}ergs/sec gives an upper bound on the neutrino magnetic dipole moment {mu}{sub {nu}}{lt}0.2{times}10{sup {minus}13}{mu}{sub {ital B}}. This is 2 orders of magnitude more stringent than the previously established bounds on {mu}{sub {nu}} from considerations of supernova cooling rate by right-handed neutrinos. {copyright} {ital 1996 The American Physical Society.}