Gravitational dynamics of an infinite shuffled lattice: early time evolution and universality of nonlinear...

In two recent papers, a detailed study has been presented of the out-of-equilibrium dynamics of an infinite system of self-gravitating points initially located on a randomly perturbed lattice. In this paper, we extend the treatment of the early time phase during which strong nonlinear correlations first develop, prior to the onset of "self-similar" scaling in the two-point correlation function. We establish more directly, using appropriate modifications of the numerical integration, that the development of these correlations can be well described by an approximation of the evolution in two phases: a first perturbative phase in which particle displacements are small compared to the lattice spacing, and a subsequent phase in which particles interact only with their nearest neighbors. For the range of initial amplitudes considered, we show that the first phase can be well approximated as a transformation of the perturbed lattice configuration into a Poisson distribution at the relevant scales. This appears to explain the universality of the spatial dependence of the asymptotic nonlinear clustering observed from both shuffled lattice and Poisson initial conditions.