N-point correlations in CDM and $\Omega$CDM Simulations

Higher order statistics are investigated in ($\Omega$)CDM universes by analyzing $500\mpc$ high resolution tree N-body simulations with both $\Omega = 1$, and $\Omega < 1$. The amplitudes of the N-point correlation functions are calculated from moments of counts-in-cells determined by a pair of new algorithms especially developed for large simulations. This approach enables massive oversampling with $\simeq 10^{9-14}$ cells for accurate determination of factorial moments from up to 47 million particles in the scale range of $8 \kpc - 125\mpc$. Thorough investigation shows that there are three scale ranges in the simulations: $\ge 8\mpc$, weakly non-linear regime, where perturbation theory applies with utmost precision, $1\mpc - 8\mpc$, the non-linear plateau, and finally $\le 1\mpc$, a regime where dynamical discreteness effects dominate the higher order statistics. In the physically relevant range of $1\mpc-125\mpc$ the results i) confirm the validity of perturbation theory in the weakly non-linear regime, ii) establish the existence of a plateau in the highly non-linear regime similar to the one observed in scale free simulations iii) show extended perturbation theory to be an excellent approximation for the non-linear regime iv) find the time dependence of the $S_N$'s to be negligible in both regimes v) in comparison with similar measurements in the EDSGC survey, strongly support $\Omega < 1$ with no biasing vi) show that the formulae of Szapudi & Colombi (1996) provide a good approximation for errors on higher order statistics measured in N-body simulations.