Fast route to nonlinear clustering statistics in modified gravity theories

Abstract

We propose a simple and computationally fast method for performing $N$-body simulations for a large class of modified gravity theories with a screening mechanism such as chameleons, symmetrons, and Galileons. By combining the linear Klein--Gordon equation with a screening factor, calculated from analytical solutions of spherical symmetric configurations, we obtain a modified field equation of which the solution is exact in the linear regime while at the same time taking screening into account on nonlinear scales. The resulting modified field equation remains linear and can be solved just as quickly as the Poisson equation without any of the convergence problems that can arise when solving the full equation. We test our method with $N$-body simulations and find that it compares remarkably well with full simulations well into the nonlinear regime.