The coincidence problem in cosmology

Interacting quintessence models have been proposed to explain or, at least alleviate, the coincidence problem of late cosmic acceleration. We show that it is possible to construct models that give rise to three different epochs: radiation, matter and accelerated, lasting long enough to allow the emergence of large scale structure. We confront our model with data on Cosmic Microwave Background temperature anisotropies, matter power spectrum and Supernovae type Ia luminosity distances and find that the data are only capable of setting upper limits on the interaction. We show how the integrated Sachs-Wolfe effect could provide indirect evidence of the existence of the interaction but, at present, the prospects that the coincidence problem can be explained by the coupling of dark matter to dark energy are not statistically favored by the data. © 2008 EAS EDP Sciences.