Sensitivity of the gamma-ray method for strong primordial magnetic fields

Abstract

Primordial magnetic field with the strength in 1-10 pG range can resolve the tension between different measurements of the Hubble constant and provide explanation for the excess opacity in 21 cm line at redshift 15 < < 20, if it is present during recombination and reionisation 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 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 the strength 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 reionisation epochs.

ICRC 2021: Gamma-ray Direct Rapporteur

“…H.E.S.S has produced new constraints on the IGMF [27]. Finally, there are new constraints on cosmological magnetic fields [28].…”