Numerical analyses of weakly nonlinear velocity-density coupling

We study the evolution of various statistical quantities of smoothed cosmic density and velocity fields using N-body simulations. The parameter C = [V (2)delta]/[V-2][delta (2)]) characterizes the nonlinear coupling of these t wo fields, and determines the behavior of the bulk velocity dispersion as a function of the local density contrast. We find that this parameter depend s strongly on the smoothing scale, even in quasilinear regimes in which the skewness parameter S-3 = [delta (3)]/[delta (2)](2) is nearly constant, an d is close to the value predicted by second-order perturbation theory. We a lso analyze weakly nonlinear effects caused by an adaptive smoothing known as the "gather approach."