New probe of magnetic fields in the prereionization epoch. I. Formalism

Understand

We propose a method of measuring extremely weak magnetic fields in the intergalactic medium prior to and during the epoch of cosmic reionization.

• The method utilizes the Larmor precession of spin-polarized neutral hydrogen in the triplet state of the hyperfine transition.
• This precession leads to a systematic change in the brightness temperature fluctuations of the 21-cm line from the high-redshift universe, and thus the statistics of these fluctuations encode information about the magnetic field the atoms are immersed in.
• The method is most suited to probing fields that are coherent on large scales; in this paper, we consider a homogenous magnetic field over the scale of the 21-cm fluctuations.