Time-dependent couplings in the dark sector: from background evolution to non-linear structure formation

We present complete numerical study of cosmological models with a -dependent coupling between the dark energy component driving the accelerated expansion of the Universe and the cold dark matter (CDM) fluid. Depending on the functional form of the coupling strength, models show a range of possible intermediate behaviours between standard ΛCDM background evolution and the widely studied of interacting dark energy models with a constant coupling. These background evolutions play a crucial role in the growth of structures and determine strikingly different effects of the on the internal dynamics of non-linear objects. By means of a modification of the cosmological N-body code GADGET-2, we have a series of high-resolution N-body simulations of structure in the context of interacting dark energy models with variable. Depending on the type of background evolution, the halo profiles are found to be either less or more concentrated with to ΛCDM, contrarily to what happens for constant coupling where concentrations can only decrease. However, for some choice of the interaction function, the reduction in halo can be larger than in constant coupling scenarios. We find that different types of coupling evolution determine specific in the growth of large-scale structures, like peculiar of the matter power spectrum shape or different -evolutions of the halo mass function. Furthermore, also for -dependent couplings, baryons and CDM develop a bias already on scales, which is progressively enhanced for smaller and smaller, and the effect can be significantly larger compared to constant scenarios. The same happens to the baryon fraction of haloes, can be more significantly reduced below its universal value in coupling models with respect to constant coupling cosmologies. general, we find that time-dependent interactions between dark energy CDM can in some cases determine stronger effects on structure as compared to the constant coupling case, with a weaker impact on the background evolution of the universe, might therefore provide a more viable possibility to alleviate the between observations and the ΛCDM model on small scales the constant coupling scenario.