Testing coupled dark energy models with their cosmological background
  evolution
  We consider a cosmology in which dark matter and a quintessence scalar field
responsible for the acceleration of the Universe are allowed to interact.
Allowing for both conformal and disformal couplings, we perform a global
analysis of the constraints on our model using Hubble parameter measurements,
baryon acoustic oscillation distance measurements, and a Supernovae Type Ia
data set. We find that the additional disformal coupling relaxes the conformal
coupling constraints. Moreover we show that, at the background level, a
disformal interaction within the dark sector is preferred to both $\Lambda$CDM
and uncoupled quintessence, hence favouring interacting dark energy.
