Probing Modified Gravity by Combining Supernovae and Galaxy Cluster   Surveys
  Possible explanations of the observed accelerated expansion of the Universe are the introduction of a dark energy component or the modifications of gravity at large distances. A particular difference between these scenarios is the dynamics of the growth of structures. The redshift distribution of galaxy clusters will probe this growth of structures with large precision. Here we will investigate how proposed galaxy cluster surveys will allow one to distinguish the modified gravity scenarios from dark energy models. We find that cluster counts can distinguish the Dvali-Gabadadze-Porrati model from a dark energy model, which has the same background evolution, as long as the amplitude of the primordial power spectrum is constrained by a CMB experiment like Planck. In order to achieve this, only a couple of hundred clusters in bins of width Delta-z = 0.1 are required. This should be easily achievable with forthcoming Sunyaev-Zel'dovich cluster counts, such as the South Pole Telescope in conjunction with the Dark Energy Survey. 
Jia-Yu Tang, Jochen Weller and Alan Zablocki