Conformal Transformations and Accelerated Cosmologies
  A cosmological theory that predicts a late-time accelerated attractor with a constant dark matter to dark energy ratio can be said to solve the Coincidence Problem. Such cosmologies are naturally generated in the context of non-standard gravity theories under conformal transformation because of the resulting couplings between scalar fields and matter. The present work examines four classes of these transformed theories and finds that only a small subset--those with a single scalar field--are capable of solving the Coincidence Problem. 
James L. Crooks and Paul H. Frampton