Dark Matter from R^2-gravity
  The modification of Einstein gravity at high energies is mandatory from a quantum approach. In this work, we point out that this modification will necessarily introduce new degrees of freedom. We analyze the possibility that these new gravitational states can provide the main contribution to the non-baryonic dark matter of the Universe. Unfortunately, the right ultraviolet completion of gravity is still unresolved. For this reason, we will illustrate this idea with the simplest high energy modification of the Einstein-Hilbert action: R^2-gravity. 
Jose A. R. Cembranos