Self-consistent cosmological simulations of DGP braneworld gravity

We perform cosmological N-body simulations of the Dvali-Gabadadze-Porrati (DGP) braneworld model, by solving the full nonlinear equations of motion for the scalar degree of freedom in this model, the brane-bending mode. While coupling universally to matter, the brane-bending mode has self-interactions that become important as soon as the density field becomes nonlinear. These self-interactions lead to a suppression of the field in high-density environments, and restore gravity to general relativity. The code uses a multigrid relaxation scheme to solve the nonlinear field equation in the quasistatic approximation. We perform simulations of a flat self-accelerating DGP model without cosmological constant. However, the type of nonlinear interactions of the brane-bending mode, which are the focus of this study, are generic to a wide class of braneworld cosmologies. The results of the DGP simulations are compared with standard gravity simulations assuming the same expansion history, and with DGP simulations using the linearized equation for the brane-bending mode. This allows us to isolate the effects of the nonlinear self-couplings of the field which are noticeable already on quasilinear scales. We present results on the matter power spectrum and the halo mass function, and discuss the behavior of the brane-bending mode within cosmological structure formation. We find that, independently of cosmic microwave background constraints, the self-accelerating DGP model is strongly constrained by current weak lensing and cluster abundance measurements.