Neutrino-electron magnetohydrodynamics in an expanding Universe

TL;DR

This paper develops a new neutrino-electron magnetohydrodynamics model in an expanding universe, revealing how neutrino motion can generate magnetic fields during the early universe's evolution.

Contribution

The paper introduces a novel fluid model for neutrino-plasma interactions in cosmology, incorporating collective effects and deriving new magnetic field source terms.

Findings

Neutrino motion influences plasma dynamics via a ponderomotive force.

New terms in the induction equation can generate magnetic fields.

Model applicable to different epochs of the early universe.

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 multi-species 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 inertia-less electrons to obtain a set of neutrino-electron magnetohydrodynamics (NEMHD) 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.