Light scalaron as dark matter

A new cosmological scenario is proposed in which a light scalaron of $f (R)$ gravity plays the role of dark matter. In this scenario, the scalaron initially resides at the minimum of its effective potential while the electroweak symmetry is unbroken. At the beginning of the electroweak crossover, the evolving expectation value of the Higgs field triggers the evolution of the scalaron due to interaction between these fields. After the electroweak crossover, the oscillating scalaron can represent cold dark matter. Its current energy density depends on a single free parameter, the scalaron mass $m$, and the value $m \simeq 4 \times 10^{-3}\, \text{eV}$ is required to explain the observed dark-matter abundance. Larger mass values would be required in scenarios where the scalaron is excited before the electroweak crossover.