Indications of a late-time interaction in the dark sector
  We show that a general late-time interaction between cold dark matter and
vacuum energy is favoured by current cosmological datasets. We characterize the
strength of the coupling by a dimensionless parameter $q_V$ that is free to
take different values in four redshift bins from the primordial epoch up to
today. This interacting scenario is in agreement with measurements of cosmic
microwave background temperature anisotropies from the Planck satellite,
supernovae Ia from Union 2.1 and redshift space distortions from a number of
surveys, as well as with combinations of these different datasets. We show that
a non-zero interaction is very likely at late times. We then focus on the case
$q_V\not=0$ in a single low-redshift bin, obtaining a nested one parameter
extension of the standard $\Lambda$CDM model. We study the Bayesian evidence,
with respect to $\Lambda$CDM, of this late-time interaction model, finding
moderate evidence for an interaction starting at $z=0.9$, dependent upon the
prior range chosen for the interaction strength parameter $q_V$. For this case
the null interaction ($q_V=0$, i.e.$\Lambda$CDM) is excluded at 99% c.l..
