Probing interaction in the dark sector
  A phenomenological attempt at alleviating the so-called coincidence problem
is to allow the dark matter and dark energy to interact. By assuming a coupled
quintessence scenario characterized by an interaction parameter $\epsilon$, we
investigate the precision in the measurements of the expansion rate $H(z)$
required by future experiments in order to detect a possible deviation from the
standard $\Lambda$CDM model ($\epsilon = 0$). We perform our analyses at two
levels, namely: through Monte Carlo simulations based on $\epsilon$CDM models,
in which $H(z)$ samples with different accuracies are generated and through an
analytic method that calculates the error propagation of $\epsilon$ as a
function of the error in $H(z)$. We show that our analytical approach traces
simulations accurately and find that to detect an interaction {using $H(z)$
data only, these must reach an accuracy better than 1%.
