Electromagnetic Form Factors of a Massive Neutrino
  Electromagnetic form factors of a massive neutrino are studied in a minimally extended standard model in an arbitrary $R_{\xi}$ gauge and taking into account the dependence on the masses of all interacting particles. The contribution from all Feynman diagrams to the charge, magnetic, and anapole form factors, in which the dependence on the masses of all particles as well as on gauge parameters is accounted for exactly, are obtained for the first time in explicit form. The asymptotic behavior of the magnetic form factor for large negative squares of the momentum of an external photon is analyzed and expression for the anapole moment of a massive neutrino is derived. The results are generalized to the case of mixing between various generations of the neutrino. Explicit expressions are obtained for the charge, magnetic, and electric dipole and anapole transition form factors as well as for the transition electric dipole moment. 
Maxim Dvornikov and Alexander Studenikin