New bound on neutrino dipole moments from globular-cluster stars

Neutrino dipole moments μ_ν would increase the core mass of red giants at the helium flash by {δ}MC=0.015M_{{{μ}}}_{{ν}}$/${10}^{{{-}}12}μB (where μB is the Bohr magneton) because of enhanced neutrino losses. Existing measurements of the bolometric magnitudes of the brightest red giants in 26 globular clusters, number counts of horizontal-branch stars and red giants in 15 globular clusters, and statistical parallax determinations of field RR Lyrae luminosities yield {δ}MC=(0.009±{}0.012)M_ so that conservatively μ_ν3×{}10^-12{{{μ}}}B$.