Splashback radius of nonspherical dark matter halos from cosmic density
  and velocity fields
  We investigate the splashback features of dark-matter halos based on cosmic
density and velocity fields. Besides the density correlation function binned by
the halo orientation angle which was used in the literature, we introduce, for
the first time, the corresponding velocity statistic, alignment momentum
correlation function, to take into account the asphericity of halos. Using
large-volume, high-resolution N-body simulations, we measure the alignment
statistics of density and velocity. On halo scales, $x\sim R_\mathrm{200m} \sim
1Mpc/h$, we detect a sharp steepening in the momentum correlation associated
with the physical halo boundary, or the splashback feature, which is found more
prominent than in the density correlation. We also find that the splashback
radius determined from the density correlation becomes $\sim 3.5\%$ smaller
than that from the momentum correlation, with their correlation coefficient
being 0.605. Moreover, the orientation-dependent splashback feature due to halo
asphericity is measured when the density profile is determined by dark-matter
particles, which can be used as a test of collisional CDM since the halo shape
is predicted to be rounder in such a model.
