Cosmic History of Chameleonic Dark Matter in $F(R)$ Gravity
  We study the cosmic history of the scalaron in $F(R)$ gravity with
constructing the time evolution of the cosmic environment and discuss the
chameleonic dark matter based on the chameleon mechanism in the early and
current Universe. We then find that the scalaron can be a dark matter. We also
propose an interesting possibility that the $F(R)$ gravity can address the
coincidence problem.
