Sensitivity reach of gamma-ray measurements for strong cosmological magnetic fields

TL;DR

This paper evaluates the capability of gamma-ray observations, specifically using CTA telescopes, to detect primordial magnetic fields in the 1-10 pG range, which could explain certain cosmological tensions and phenomena.

Contribution

It demonstrates that gamma-ray measurements can detect primordial magnetic fields up to 10^{-11} G, bridging observational constraints from CMB and gamma-ray data.

Findings

Gamma-ray technique can sense magnetic fields up to 10^{-11} G.

Combination of CMB and gamma-ray constraints covers the full range of cosmological magnetic fields.

Primordial magnetic fields could influence key epochs like recombination and reionization.

Abstract

A primordial magnetic field with the strength in the 1-10 pG range can resolve the tension between different measurements of the Hubble constant and provide an explanation for the excess opacity in the 21 cm line at redshift $15<z<20$, if it is present during the recombination and reionization epochs. This field can also survive in the voids of the large-scale Structure in the present day universe. We study the sensitivity reach of the gamma-ray technique for measurement of such relatively strong cosmological magnetic field using deep exposure(s) of the nearest hard spectrum blazar(s) with CTA telescopes. We show that the gamma-ray measurement method can sense the primordial magnetic field with a strength of up to $10^{-11}$~G. Combination of the cosmic microwave background and gamma-ray constraints can thus sense the full range of possible cosmological magnetic fields to confirm or rule out their relevance to the problem of the origin of cosmic magnetic fields, as well as their influence on recombination and reionization epochs.