Simulations of structure formation in interacting dark energy
  cosmologies
  The evidence in favor of a dark energy component dominating the Universe, and
driving its presently accelerated expansion, has progressively grown during the
last decade of cosmological observations. If this dark energy is given by a
dynamic scalar field, it may also have a direct interaction with other matter
fields in the Universe, in particular with cold dark matter. Such interaction
would imprint new features on the cosmological background evolution as well as
on the growth of cosmic structure, like an additional long-range fifth-force
between massive particles, or a variation in time of the dark matter particle
mass. We review here the implementation of these new physical effects in the
N-body code GADGET-2, and we discuss the outcomes of a series of
high-resolution N-body simulations for a selected family of interacting dark
energy models, as already presented in Baldi et al. [20]. We interestingly
find, in contrast with previous claims, that the inner overdensity of dark
matter halos decreases in these models with respect to LCDM, and consistently
halo concentrations show a progressive reduction for increasing couplings.
Furthermore, the coupling induces a bias in the overdensities of cold dark
matter and baryons that determines a decrease of the halo baryon fraction below
its cosmological value. These results go in the direction of alleviating
tensions between astrophysical observations and the predictions of the LCDM
model on small scales, thereby opening new room for coupled dark energy models
as an alternative to the cosmological constant.
