Constraining f(R) Gravity as a Scalar Tensor Theory
  We search for viable f(R) theories of gravity, making use of the equivalence between such theories and scalar-tensor gravity. We find that models can be made consistent with solar system constraints either by giving the scalar a high mass or by exploiting the so-called chameleon effect. However, in both cases, it appears likely that any late-time cosmic acceleration will be observationally indistinguishable from acceleration caused by a cosmological constant. We also explore further observational constraints from, e.g., big bang nucleosynthesis and inflation. 
Thomas Faulkner (MIT), Max Tegmark (MIT), Emory F. Bunn (Richmond), Yi   Mao (MIT)