  If the accelerated expansion of the Universe at the present epoch is driven
by a dark energy scalar field, there may well be a non-trivial coupling between
the dark energy and the cold dark matter (CDM) fluid. Such interactions give
rise to new features in cosmological structure growth, like an additional
long-range attractive force between CDM particles, or variations of the dark
matter particle mass with time. We have implemented these effects in the N-body
code GADGET-2 and present results of a series of high-resolution N-body
simulations where the dark energy component is directly interacting with the
cold dark matter. As a consequence of the new physics, CDM and baryon
distributions evolve differently both in the linear and in the nonlinear regime
of structure formation. Already on large scales a linear bias develops between
these two components, which is further enhanced by the nonlinear evolution. We
also find, in contrast with previous work, that the density profiles of CDM
halos are less concentrated in coupled dark energy cosmologies compared with
LCDM, and that this feature does not depend on the initial conditions setup,
but is a specific consequence of the extra physics induced by the coupling.
Also, the baryon fraction in halos in the coupled models is significantly
reduced below the universal baryon fraction. These features alleviate tensions
between observations and the LCDM model on small scales. Our methodology is
ideally suited to explore the predictions of coupled dark energy models in the
fully non-linear regime, which can provide powerful constraints for the viable
parameter space of such scenarios.
