Generation of cosmic magnetic fields in electroweak plasma

TL;DR

This paper investigates how neutrino asymmetries in a plasma can generate and amplify strong magnetic fields, potentially explaining magnetar fields and early universe magnetism through a new mechanism involving the photon polarization tensor.

Contribution

It introduces a novel mechanism for magnetic field generation via neutrino asymmetries affecting the photon polarization tensor within the Standard Model framework.

Findings

Neutrino asymmetries can induce a nonzero Chern-Simons parameter leading to magnetic field instability.

The mechanism can account for magnetar magnetic fields during supernova explosions.

A lower bound on neutrino asymmetries compatible with Big Bang nucleosynthesis is established.

Abstract

We study the generation of strong magnetic fields in magnetars and in the early universe. For this purpose we calculate the antisymmetric contribution to the photon polarization tensor in a medium consisting of an electron-positron plasma and a gas of neutrinos and antineutrinos, interacting within the Standard Model. Such a contribution exactly takes into account the temperature and the chemical potential of plasma as well as the photon dispersion law in this background matter. It is shown that a nonvanishing Chern-Simons parameter, which appears if there is a nonzero asymmetry between neutrinos and antineutrinos, leads to the instability of a magnetic field resulting to its growth. We apply our result to the description of the magnetic field amplification in the first second of a supernova explosion. It is suggested that this mechanism can explain strong magnetic fields of magnetars. Then we use our approach to study the cosmological magnetic field evolution. We find a lower bound on the neutrino asymmetries consistent with the well-known Big Bang nucleosynthesis bound in a hot universe plasma. Finally we examine the issue of whether a magnetic field can be amplified in a background matter consisting of self-interacting electrons and positrons.