Simulating the quartic Galileon gravity model on adaptively refined meshes

Abstract

We develop a numerical algorithm to solve the high-order nonlinear\nderivative-coupling equation associated with the quartic Galileon model, and\nimplement it in a modified version of the RAMSES N-body code to study the\neffect of the Galileon field on the large-scale matter clustering. The\nalgorithm is tested for several matter field configurations with different\nsymmetries, and works very well. This enables us to perform the first\nsimulations for a quartic Galileon model which provides a good fit to the\ncosmic microwave background (CMB) anisotropy, supernovae and baryonic acoustic\noscillations (BAO) data. Our result shows that the Vainshtein mechanism in this\nmodel is very efficient in suppressing the spatial variations of the scalar\nfield. However, the time variation of the effective Newtonian constant caused\nby the curvature coupling of the Galileon field cannot be suppressed by the\nVainshtein mechanism. This leads to a significant weakening of the strength of\ngravity in high-density regions at late times, and therefore a weaker matter\nclustering on small scales. We also find that without the Vainshtein mechanism\nthe model would have behaved in a completely different way, which shows the\ncrucial role played by nonlinearities in modified gravity theories and the\nimportance of performing self-consistent N-body simulations for these theories.\n