Comparing a Markov-Chain-Monte-Carlo simulation of the de Sitter attractor in generalized Proca theory with a variety of cosmological data (CMB, BAO, SNIa, low-redshift H), it is shown that the model (which has a modified dark energy equation of state) is favoured over LCDM. One can also study perturbations, and impose no-ghost and stability conditions, as well as conditions from the galactic power spectrum of redshift-space distortions.

An only indirectly observed vector field is no less natural or expected than an only indirectly observed scalar field (like the inflaton, or a dark energy field). It is therefore important to compare general vector-tensor EFTs with cosmological to data, to see how they fare compared with (more conventional) scalar-tensor models, and with the concordance model.