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.
