  In this paper, we conduct a study on the scalar field obtained from
$\mathit{f(R)}$ gravity via Weyl transformation of the spacetime metric
$g_{\mu\nu}$ from the Jordan frame to the Einstein frame. The scalar field is
obtained as a result of the modification in the geometrical part of Einstein's
field equation of General Relativity. For the Hu-Sawicki model of
$\mathit{f(R)}$ gravity, we find the effective potential of the scalar field
and calculate its mass. Our study shows that the scalar field (also named as
scalaron) obtained from this model has the chameleonic property, i.e.\ the
scalaron becomes light in the low-density region while it becomes heavy in the
high-density region of matter. Then it is found that the scalaron can be
regarded as a dark matter (DM) candidate since the scalaron mass is found to be
quite close to the mass of ultralight axions, a prime DM candidate. Thus the
scalaron in the Hu-Sawicki model of $\mathit{f(R)}$ gravity behaves as DM.
Further, a study on the evolution of the scalaron mass with the redshift is
also carried out, which depicts that scalaron becomes light with expansion of
the Universe and with different rates at different stages of the Universe.

General Relativity and Quantum Cosmology