We calculate the correction to the neutrino electromagnetic vertex due to the background of electrons in a large class of models, as the supersymmetric model with explicit breaking of R parity, where charged scalar bosons couple to leptons and which are able to provide an astrophysically interesting value for the neutrino magnetic (electric) moment: ${\mathrm{\mu }}_{\nu }$∼${10}^{\mathrm{-}12}$${\mathrm{\mu }}_{\mathit{B}}$. We show that the medium contribution to the chirality-flipping magnetic (electric) dipole moment is not significant; however, a new chirality-flipping, but helicity-conserving, term arises which does not appear in the standard model with the exchange of W gauge bosons. It signals the presence of CP and CPT asymmetries in the medium and can contribute to the emission or absorption of longitudinal photons. We estimate the contribution of this new term to the rate of the plasmon decay process ${\gamma }_{\mathrm{pl}}$→νν in the core of degenerate stars, showing that it can be comparable to the contribution coming from the vacuum magnetic (dipole) moment. We also calculate the correction to the effective potential of a propagating neutrino in the presence of a magnetic field due to a chirality-preserving contribution to the diagonal magnetic moment from the medium. This contribution is identical for particles and antiparticles and so it need not vanish for Majorana neutrinos.

• Received 24 November 1993

DOI:https://doi.org/10.1103/PhysRevD.50.2139