Dark matter and dark energy from a single scalar field and cosmic microwave background data

Axions are likely to be the dark matter (DM) that cosmological data require. They arise in the Peccei-Quinn solution of the strong-CP problem. In a previous work we showed that their model has a simple and natural generalization that also yields dark energy (DE), in fair proportions, without tuning any parameter: DM and DE arise from a single scalar field and are weakly coupled in the present era. In this paper we extend the analysis of this dual-axion cosmology and fit it to WMAP data, by using a Markov chain technique. We find that ΛCDM, dynamical DE with a SUGRA potential, DE with a SUGRA potential and a constant DE-DM coupling, and the dual-axion model with a SUGRA potential fit data with a similar accuracy. The best-fit parameters are, however, fairly different, although consistency is mostly recovered at the 2 σ level. A peculiarity of the dual-axion model with a SUGRA potential is to cause more stringent constraints on most parameters and to favor high values of the Hubble parameter.