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Elastic neutrino - electron scattering and potential effects of magnetic and electric dipole moments

We consider elastic neutrino - electron scattering of solar neutrinos with magnetic moments and electric dipole moments, where the solar neutrino state at the scattering site is determined by the evolution in matter and solar magnetic fields of the initial electron neutrino state. We present the general cross section for an arbitrary superposition of active and sterile neutrino types with positive and negative helicities, with particular emphasis on the effect of transverse polarization, which gives rise to an azimuthal asymmetry as a function of the recoil electron momentum. Within our physically motivated approximation, we perform a general CP analysis and show that in the 1-Dirac and 2-Majorana neutrino cases no CP-violating effects are present, which means that it is not possible to distinguish between magnetic and electric dipole moments in these cases. We also study the consequences of neutrino energy averaging on the cross section and stress that in the 2-Majorana neutrino case this averaging leads to a suppression of the transverse neutrino polarization effects.