Description
During the pre-reionization epoch, a primordial magnetic field (PMF) is
expected to influence 21-cm physics via two distinct physical pathways, namely
magnetic heating of the intergalactic medium through ambipolar diffusion and
decaying turbulence, and modification of the star formation rate through
small-scale enhancement of matter power. In this talk, I shall discuss a recent work
of ours where both effects have been integrated within a common analytic
framework, which has subsequently been used to provide upper bounds on the
PMF parameter space in the light of the global 21-cm signal reported by EDGES.
This leads to a typical upper limit of 10 pG on a nearly scale-invariant PMF, which
is strongly competitive with bounds obtained from other cosmological datasets
available at present. Our forecast analysis for the upcoming SKA-Low facility
sheds light on the prospect of further constraining the PMF window that is
consistent with the EDGES observation, projecting $1\sigma$ errors
$\lesssim10\%$ on the relevant PMF parameters and an associated
signal-to-noise ratio (SNR) $\gtrsim10$. During the post-reionization epoch, on the
other hand, the PMF-enhanced matter power on small scales is expected to
strongly affect the Lyman-$\alpha$ power spectrum and cross-correlations
between Lyman-$\alpha$ and 21-cm fluctuations, which may thus serve as
important probes of the PMF sector at late times. I shall conclude by briefly
discussing our ongoing work in this direction in the light of upcoming 21-cm and
large scale survey missions.
