Early massive clusters and the bouncing coupled dark energy
  The abundance of the most massive objects in the Universe at different epochs
is a very sensitive probe of the cosmic background evolution and of the growth
history of density perturbations, and could provide a powerful tool to
distinguish between a cosmological constant and a dynamical dark energy field.
In particular, the recent detection of very massive clusters of galaxies at
high redshifts has attracted significant interest as a possible indication of a
failure of the standard LCDM model. Several attempts have been made in order to
explain such detections in the context of non-Gaussian scenarios or interacting
dark energy models, showing that both these alternative cosmologies predict an
enhanced number density of massive clusters at high redshifts, possibly
alleviating the tension. However, all the models proposed so far also
overpredict the abundance of massive clusters at the present epoch, and are
therefore in contrast with observational bounds on the low-redshift halo mass
function. In this paper we present for the first time a new class of
interacting dark energy models that simultaneously account for an enhanced
number density of massive clusters at high redshifts and for both the standard
cluster abundance at the present time and the standard power spectrum
normalization at CMB. The key feature of this new class of models is the
"bounce" of the dark energy scalar field on the cosmological constant barrier
at relatively recent epochs. We present the background and linear perturbations
evolution of the model, showing that the standard amplitude of density
perturbations is recovered both at CMB and at the present time, and we
demonstrate by means of large N-body simulations that our scenario predicts an
enhanced number of massive clusters at high redshifts without affecting the
present halo abundance. (Abridged)
