Freeze-in production of scalaron dark matter in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mrow> <mml:mi>f</mml:mi> <mml:mo stretchy="false">(</mml:mo> <mml:mi>R</mml:mi> <mml:mo stretchy="false">)</mml:mo> </mml:

We demonstrate that the scalaron, a scalar degree of freedom, emerging from the <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"> <a:mi>f</a:mi> <a:mo stretchy="false">(</a:mo> <a:mi>R</a:mi> <a:mo stretchy="false">)</a:mo> </a:math> theory of gravity, can account for the observed dark matter (DM) abundance if its mass is around the MeV scale, to ensure its cosmological stability. Focusing on two well-known <e:math xmlns:e="http://www.w3.org/1998/Math/MathML" display="inline"> <e:mi>f</e:mi> <e:mo stretchy="false">(</e:mo> <e:mi>R</e:mi> <e:mo stretchy="false">)</e:mo> </e:math> gravity models, we systematically show that if scalaron production proceeds via the freeze-in mechanism, the right relic abundance is satisfied over a very narrow window of reheating temperature <i:math xmlns:i="http://www.w3.org/1998/Math/MathML" display="inline"> <i:msup> <i:mn>10</i:mn> <i:mn>14</i:mn> </i:msup> <i:mo>≲</i:mo> <i:msub> <i:mi>T</i:mi> <i:mrow> <i:mi>rh</i:mi> </i:mrow> </i:msub> <i:mo>≲</i:mo> <i:msup> <i:mn>10</i:mn> <i:mn>16</i:mn> </i:msup> <i:mtext> </i:mtext> <i:mtext> </i:mtext> <i:mi>GeV</i:mi> </i:math> . We delineate the viable parameter space of the <k:math xmlns:k="http://www.w3.org/1998/Math/MathML" display="inline"> <k:mi>f</k:mi> <k:mo stretchy="false">(</k:mo> <k:mi>R</k:mi> <k:mo stretchy="false">)</k:mo> </k:math> models consistent with the observed DM abundance, and highlight relevant experimental constraints from searches targeting DM decay signatures.