Dark matter in modified gravity?

We explore a new horizon of modified gravity from the viewpoint of particle physics. As a concrete example, we take the $F(R)$ gravity to raise a question: can a scalar particle (``scalaron'') derived from the $F(R)$ gravity be a dark matter candidate? We place the limit on the parameter in a class of $F(R)$ gravity model from the constraint on the scalaron as a dark matter. The role of the screening mechanism and compatibility with the dark energy problem are addressed.