Freeze-in production of scalaron dark matter in $f(R)$ gravity

TL;DR

This paper explores how the scalaron from $f(R)$ gravity can serve as dark matter produced via freeze-in, with the correct relic abundance achieved in a narrow reheating temperature window, constrained by decay searches.

Contribution

It systematically analyzes scalaron production via freeze-in in two $f(R)$ models, identifying the parameter space compatible with observed dark matter abundance.

Findings

Scalaron can account for dark matter at MeV mass scale.

Relic abundance is achieved within a narrow reheating temperature window.

Experimental constraints from decay signatures limit viable models.

Abstract

We demonstrate that the scalaron, a scalar degree of freedom, emerging from the $f(R)$ 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 $f(R)$ 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 $10^{14}\lesssim T_{\rm rh}\lesssim 10^{16}$ GeV. We delineate the viable parameter space of the $f(R)$ models consistent with the observed DM abundance, and highlight relevant experimental constraints from searches targeting DM decay signatures.