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Abstract

We derive a new model for neutrino-plasma interactions in an expanding
universe that incorporates the collective effects of the neutrinos on
the plasma constituents. We start from the kinetic description of a
multispecies plasma in the flat Friedmann-Robertson-Walker metric, where
the particles are coupled to neutrinos through the charged- and
neutral-current forms of the weak interaction. We then derive the fluid
equations and specialize our model to (a) the lepton epoch, where we
consider a pair electron-positron plasma interacting with electron
(anti)neutrinos, and (b) after the electron-positron annihilation, where
we model an electron-proton plasma and take the limit of slow ions and
inertialess electrons to obtain a set of neutrino-electron
magnetohydrodynamics equations. In both models, the dynamics of the
plasma is affected by the neutrino motion through a ponderomotive force
and, as a result, new terms appear in the induction equation that can
act as a source for magnetic field generation in the early Universe. A
brief discussion on the possible applications of our model is proposed.