http://arxiv.org/abs/2203.03573
It has been suggested that the weak magnetic field hosted by the intergalactic medium (IGM) in voids could be a relic from the early Universe. However, accepted models of turbulent magnetohydrodynamic (MHD) decay predict that the present-day strength of fields generated at the electroweak phase transition (EWPT) should be too low to explain the observed scattering of $\gamma$-rays from TeV blazars. Here, we apply recent theoretical developments — namely, the discovery of the Saffman helicity invariant and of the role of magnetic reconnection in setting the decay rate — to show that the accepted models greatly underpredict the present-day strength of relic fields. Our estimates restore the consistency of the EWPT-relic hypothesis with observational constraints; moreover, we find that efficient magnetogenesis at the EWPT could produce relics with the strength that is believed sufficient to resolve the Hubble tension and explain galaxy-cluster magnetic fields without invoking dynamo amplification.
D. Hosking and A. Schekochihin
Tue, 8 Mar 22
67/100
Comments: 19 pages, including supplementary information; 6 figures