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## Electromagnetic Properties

A neutrino electromagnetic dipole or transition moment would lead to an enhanced rate for the plasma decay process  which dominates the neutrino cooling of low-mass stars, notably of low-mass red giants before the helium flash. This would delay helium ignition, in contradiction with globular-cluster data, leading to
 (1.7)

with  the Bohr magneton. This limit applies if  where threshold effects become important. Transition moments can be constrained by searching for radiative decays . If  is essentially massless the decay rate is  with  the transition moment. If neutrinos obey Eq. () the phase-space factor  renders the radiative decay limits from reactor, accelerator, solar, supernova, and cosmic background neutrinos less restrictive than Eq. ().

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