Slow decay of magnetic fields in open Friedmann universes

TL;DR

This paper explains how magnetic fields in open Friedmann universes decay more slowly than in flat models due to relativistic effects, potentially leading to stronger primordial magnetic fields.

Contribution

It demonstrates that relativistic coupling causes superadiabatic growth of magnetic fields in open universes, a novel insight into cosmic magnetic field evolution.

Findings

Magnetic fields decay slower in open universes compared to flat models.

Relativistic effects cause superadiabatic amplification of magnetic fields.

Potential for significant primordial magnetic fields in marginally open universes.

Abstract

We describe how magnetic fields in Friedmann universes can experience superadiabatic growth without departing from conventional electromagnetism. The reason is the relativistic coupling between vector fields and spacetime geometry, which slows down the decay of large-scale magnetic fields in open universes, compared to that seen in perfectly flat models. The result is a large relative gain in magnetic strength during the pre-galactic era that can lead to astrophysically interesting B-fields, even if our universe is only marginally open today.