Early Growth in a Perturbed Universe: Exploring Dark Matter Halo
  Populations in 2LPT and ZA Simulations
  We study the structure and evolution of dark matter halos from z = 300 to z =
6 for two cosmological N-body simulation initialization techniques. While the
second order Lagrangian perturbation theory (2LPT) and the Zel'dovich
approximation (ZA) both produce accurate present day halo mass functions,
earlier collapse of dense regions in 2LPT can result in larger mass halos at
high redshift. We explore the differences in dark matter halo mass and
concentration due to initialization method through three 2LPT and three ZA
initialized cosmological simulations. We find that 2LPT induces more rapid halo
growth, resulting in more massive halos compared to ZA. This effect is most
pronounced for high mass halos and at high redshift. Halo concentration is, on
average, largely similar between 2LPT and ZA, but retains differences when
viewed as a function of halo mass. For both mass and concentration, the
difference between typical individual halos can be very large, highlighting the
shortcomings of ZA-initialized simulations for high-z halo population studies.
