Viability of the cluster mass function formalism in parametrised   modified gravity
  Model-independent parametrisations for examining departures from General Relativity have been increasingly studied over the past few years. Various observables have been used to constrain the parameters and forecasts for future surveys have been carried out. In one such forecast, galaxy cluster counts were used to constrain the parameters. Here, we carry out a limited set of $N$-body simulations, with a modified Poisson equation, to examine the accuracy of existing mass functions for modified gravity cosmologies. As well as altering the gravitational calculation, we include the effect of a screening scale to ensure consistency of the theory with solar system tests. Our results suggest that if a screening scale exists its effect can be taken into account in the cluster count calculation through its effect on the linear matter power spectrum. If this is done, the accuracy of the standard mass function formalism in modified gravity theories with reasonably small departures from General Relativity, as tested in this work, is comparable to the standard case. 
Daniel B. Thomas and Carlo R. Contaldi
astro-ph.CO