Cosmic Neutrino Background as a Ferromagnet

TL;DR

This paper proposes that cosmic background neutrinos could have undergone a ferromagnetic phase transition, creating a primordial magnetic field that may seed galactic magnetic fields, contingent on neutrino interactions beyond the Standard Model.

Contribution

It introduces a novel mechanism where neutrino spin interactions lead to ferromagnetic ordering, potentially explaining primordial magnetic seed fields in the universe.

Findings

Magnetization could occur if neutrino interactions involve a massless boson beyond the Standard Model.

Estimated magnetic seed strength ranges from approximately 10^{-27} G to 10^{-10} G.

The phase transition depends on specific coupling constants and neutrino masses.

Abstract

If cosmic background neutrinos interact very weakly with each other, through spin-spin interactions, then they may have experienced a phase transition, leading to a ferromagnetic ordering. The small magnetic field resulting from ferromagnetic ordering -- if present before galaxy formation -- could act as a primordial seed of the magnetic fields observed in several galaxies. Our findings suggest that the magnetization could occur in the right epoch, if the exchange boson of neutrino-neutrino interaction is a massless boson beyond the Standard Model, with a coupling constant of $2.2\times 10^{-13} \left(\frac{m_\nu}{10^{-4}\,\rm{eV}}\right)^2<g<2.3\times 10^{-7}$. The estimation of the magnetic seed is $2.3 \times 10^{-27}\,\rm{G}\lesssim B_{\rm CNB}\lesssim 6.8\times 10^{-10}G$.