Neutrino helicity flip from gravity-spin coupling

It is suggested that the rotation-spin coupling predicted by Mashhoon may lead, in the case of neutrinos, to a helicity flip that has implications for astrophysical objects such as rotating neutron stars and supernovae. The coupling is generalized here to include gravitational fields and total angular momentum and is derived by solving the covariant Dirac and Maxwell-Proca equations exactly to first order in the metric deviation ${\gamma }_{\mathrm{\mu }\nu }$. For fermions the spin part of the effect also applies to gravitational fields of arbitrary strength.