Fitting type Ia supernovae with coupled dark energy

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Abstract
We discuss the possible consistency of the recently discovered type Ia supernovae at z>1 with models in which dark energy is strongly coupled to a significant fraction of dark matter, and in which an (asymptotic) accelerated phase exists where dark matter and dark energy scale in the same way. Such a coupling has been suggested for a possible solution of the coincidence problem, and is also motivated by string cosmology models of 'late time' dilaton interactions. Our analysis shows that, for coupled dark energy models, the recent data are still consistent with acceleration starting as early as at z = 3 (to within 90% confidence level), although at the price of a large 'non-universality' of the dark energy coupling to different matter fields. Also, as opposed to uncoupled models which seem to prefer a 'phantom' dark energy, we find that a large amount of coupled dark matter is compatible with present data only if the dark energy field has a conventional equation of state w>?1.

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