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