Characterizing dark interactions with the halo mass accretion history and structural properties

We study the halo mass accretion history (MAH) and its correlation with the internal structural properties in coupled dark energy (cDE) cosmologies. To accurately predict all the non-linear effects caused by dark interactions, we use the COupled Dark Energy Cosmological Simulations (CoDECS). We measure the halo concentration at z = 0 and the number of substructures above a mass resolution threshold for each halo. Tracing the halo merging history trees back in time, following the mass of the main halo, we develop a MAH model that accurately reproduces the halo growth in term of M200 in the λcold dark matter (λCDM) Universe; we then compare the MAH in different cosmological scenarios. For cDE models with a weak constant coupling, our MAH model can reproduce the simulation results, within 10 per cent of accuracy, by suitably rescaling the normalization of the linear matter power spectrum at z = 0, σ8. However, this is not the case for more complex scenarios, like the 'bouncing cDE model, for which the numerical analysis shows a rapid growth of haloes at high redshifts, that cannot be reproduced by simply rescaling the value of σ8. Moreover, at a fixed value of σ8, CDM haloes in these cDE scenarios tend to be more concentrated and have a larger amount of substructures with respect to λCDM predictions. Finally, we present an accurate model that relates the halo concentration to the time at which it assembles half or 4 per cent of its mass. Combining this with our MAH model, we show how halo concentrations change while varying only σ8 in a λCDM Universe, at a fixed halo mass.