Cosmological models with multiple dark matter species and long-range scalar interactions

Abstract

In this talk, I have discussed the implications of a multi-component nature of cosmic Dark Matter for the observational bounds on possible long-range fifth-forces mediated by a Dark Energy scalar field. By assuming a simple internal symmetry of the Dark Matter component associated to opposite coupling "charges" of two different particle species, the effects of Dark Energy interactions on both the background and linear perturbations evolution are strongly suppressed during the whole matter dominated phase, thereby relaxing present bounds on the coupling strength. The associated attractive and repulsive fifth-forces, however, might still have a very significant impact on the nonlinear dynamics of collapsed structures. I have also described how some of these nonlinear effects are identified through dedicated cosmological N-body simulations as i) a possible fragmentation of bound Dark Matter halos into smaller objects, and ii) a consequent suppression of the nonlinear matter power at small scales. Both effects are potentially observable and might allow to further constrain the model.