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

Understand

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.