New bound on neutrino dipole moments from globular-cluster stars

Neutrino dipole moments ${\mathrm{\mu }}_{\nu }$ would increase the core mass of red giants at the helium flash by δ${\mathit{M}}_{\mathit{C}}$=0.015${\mathit{M}}_{\mathrm{\odot }}$ ${\mathrm{\mu }}_{\nu }$/${10}^{\mathrm{-}12}$ ${\mathrm{\mu }}_{\mathit{B}}$ (where ${\mathrm{\mu }}_{\mathit{B}}$ 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${\mathit{M}}_{\mathit{C}}$=(0.009±0.012)${\mathit{M}}_{\mathrm{\odot }}$ so that conservatively ${\mathrm{\mu }}_{\nu }$<3×${10}^{\mathrm{-}12}$ ${\mathrm{\mu }}_{\mathit{B}}$.