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.

Figure 1

The scalaron lifetime as a function of the mass in unit of GeV. The lifetime has been computed by summing up the partial decay widths in Eqs. (b2) and (b4) relevant to the mass range displayed here. The horizontal (red) dashed line corresponds to the age of the universe $\simeq 10^{17}\mathrm{s}$.

Figure 2

The Feynman graphs relevant to the $\phi \to \gamma \gamma$ decay processes. The W boson loop graphs have been drawn in the unitary gauge.

Figure 3

The Feynman graphs relevant to the $\phi \to gg$ decay processes.