  We study the constraints on the primordial magnetic fields in light of Dark
Ages global 21-cm signal. An early absorption signal in the redshift of $200
\leq z \leq 30$ is predicted in the $\Lambda\rm CDM$ model of cosmology. During
the Dark Ages, there were no stars, therefore, measuring the global 21-cm
signal can provide pristine cosmological information. However, measuring the
Dark Ages global 21-cm signal from ground-based telescopes is challenging. To
overcome this difficulty, recently lunar and space-based experiments have been
proposed, such as FARSIDE, DAPPER, FarView, etc. Primordial magnetic fields can
heat the intergalactic medium gas via magnetohydrodynamic effects. We study the
effects of magnetic fields on the Dark Ages global 21-cm signal and constrain
the present-day strength of primordial magnetic fields and the spectral index.
We find that measuring the Dark Ages signal can provide stronger bounds
compared to the existing constraints from Planck 2016. Additionally, we also
explore the dark-ages consistency ratio which can identify the magnetic heating
of IGM by measuring the 21-cm signal at only three different redshifts in
future experiments.
