Instabilities in dark coupled models and constraints from cosmological
  data
  Coupled dark matter-dark energy systems can suffer from non-adiabatic
instabilities at early times and large scales. In these proceedings, we
consider two parameterizations of the dark sector interaction. In the first one
the energy-momentum transfer 4-vector is parallel to the dark matter 4-velocity
and in the second one to the dark energy 4-velocity. In these cases, coupled
models which suffer from non-adiabatic instabilities can be identified as a
function of a generic coupling Q and of the dark energy equation of state. In
our analysis, we do not refer to any particular cosmic field. We confront then
a viable class of models in which the interaction is directly proportional to
the dark energy density and to the Hubble rate parameter to recent cosmological
data. In that framework, we show that correlations between the dark coupling
and several cosmological parameters allow for a larger neutrino mass than in
uncoupled models.
