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

Abstract 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 ( β = 0.03, 0.05 and 0.08) as well as for the standard ΛCDM cosmology ( β = 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 × 10 13 h -1 M ⊙ 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 ΛCDM 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 β increases. Meanwhile, the amplitude of V ( r ) exhibits little dependence on β , which is ascribed to the identical Hubble parameters shared by the ΛCDM and CIDER models in the entire redshift range. Our results imply that the bound-zone velocity slope can break a degeneracy even between the ΛCDM and CIDER models with β ≤ 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 β , 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.