EDGES signal in presence of magnetic fields

TL;DR

This paper investigates how primordial helical magnetic fields influence the 21-cm signal during the epoch of reionization, deriving bounds on magnetic field strength using EDGES data without invoking new dark matter physics.

Contribution

It introduces the role of primordial helical magnetic fields and the $ ext{α}$-effect in explaining the EDGES signal, providing new bounds on magnetic field strengths in the early universe.

Findings

Primordial magnetic fields are constrained between 5×10^{-4} nG and 6×10^{-3} nG.

The $ ext{α}$-effect can lower gas temperature to 3.2 K at z=17.

Results do not depend on new dark matter physics.

Abstract

We study the 21-cm differential brightness temperature in the presence of primordial helical magnetic fields for redshift $z=10-30$. We argue that the $\alpha$-effect that sets in at earlier time can be helpful in lowering the gas temperature to 3.2 degrees Kelvin at $z=17$. This effect can arise in the early Universe due to some parity violating high energy processes. Using the EDGES (Experiment to Detect the Global Epoch of Reionization Signature) results, we find the upper and lower limits on the primordial magnetic field to be $6\times 10^{-3}~{\rm nG} $ & $5\times 10^{-4}~{\rm nG}$ respectively. We also discuss the effect of Ly$\alpha$ background on the bounds. Our results do not require any new physics in terms of dark matter.