Fundamental Discreteness Limitations of CosmologicalN‐Body Clustering Simulations

Fundamental physical considerations and past tests suggest that there may be a problem with discreteness error in N–body methods widely used in cosmological clustering studies. This could cause problems with accuracy when coupled to hydrodynamics codes. We therefore investigate some of the effects that discreteness and two–body scattering may have on N-body simulations with “realistic ” cosmological initial conditions. We use an identical subset of particles from the initial conditions for a 128 3 Particle–Mesh (PM) calculation as the initial conditions for a variety of Particle–Particle–Particle Mesh (P 3 M) and Tree code runs. The force softening length and particle number in the P 3 M and Tree code runs are varied and results are compared with those of the PM run. In particular, we investigate the effect of mass resolution (or equivalently the mean interparticle separation) since most “high resolution ” codes only have high resolution in gravitational force, not in mass. We show the evolution of a wide variety of statistical measures.