The impact of constrained interacting dark energy on the bound-zone velocity profile

We numerically study the effects of constrained interacting dark energy (CIDER) on the bound-zone velocity profiles around massive dark matter halos. Analyzing the CIDER simulations performed by ref. [1] for three different cases of dark sector coupling (beta = 0.03, 0.05 and 0.08) as well as for the standard ACDM cosmology (beta = 0), we determine the mean peculiar velocity profiles in the bound zones around the friends-of-friends halos with masses larger than M cut = 3 x 1013 h - 1 M circle dot at three redshifts, z = 0, 0.5 and 1. It is found that the universal power-law formula proposed by ref. [2] originally for the ACDM case still describes well the bound-zone velocity profiles, V(r), even in the CIDER models. The slope of V(r), turns out to be significantly affected by the CIDER, progressively decreasing as beta increases. Meanwhile, the amplitude of V(r) exhibits little dependence on beta, which is ascribed to the identical Hubble parameters shared by the ACDM and CIDER models in the entire redshift range. Our results imply that the bound-zone velocity slope can break a degeneracy even between the ACDM and CIDER models with beta <= 0.03, which the standard cosmological diagnostics fail to distinguish. We devise a simple analytic formula for the bound-zone slope as a function of beta, and prove its validity at all of the three redshifts. It is concluded that the slope of the mean bound-zone peculiar velocity profile should be in principle a powerful probe of dark sector interaction.