Magnetic or electric dipole moments of neutrinos are indicators for possible extensions of the standard weak-interaction model. Certain values were recently proposed to explain the time variation in the detected solar-neutrino flux and an extragalactic background of ionizing radiation. Here we give a detailed analysis of their implications for a stellar collapse. We find two independent new upper bounds of 1.5×${10}^{\mathrm{-}12}$${\mu }_B$ and 6×${10}^{\mathrm{-}12}$${\mu }_B$ on the dipole moment of electron neutrinos, improving the existing bounds by one to two orders of magnitude and ruling out the proposed solar-neutrino effect. For values ≳${10}^{\mathrm{-}13}$${\mu }_B$ the coherently enhanced dipole scattering on the large nuclei in a collapsing star would flip the trapped left-handed neutrinos into right-handed ones, which would escape in a highly energetic prebounce ${\nu }_e$ ‘‘collapse burst.’’ This also reduces the trapped lepton number of the collapsing star. We calculate the spectra of the emitted neutrinos and the associated lepton-number decrease. From the supernova 1987A up to 100 neutrinos from this additional output should have been detected in the Kamiokande II detector. The absence of such events imposes the upper &<1.5×${10}^{\mathrm{-}12}$${\mathrm{\mu }}_{\mathrm{B}}$. In addition, the associated lepton-number decrease in the collapsing star would later, after the bounce, lead to an excessive reduction of the shock energy, so that eventually no supernova explosions would be possible. This can be avoided &<6×${10}^{\mathrm{-}12}$${\mathrm{\mu }}_{\mathrm{B}}$, providing an independent supplementary bound.

• Received 26 April 1988

DOI:https://doi.org/10.1103/PhysRevD.38.1658