A gauge-invariant approach to interactions in the dark sector

Abstract

We outline a gauge-invariant framework to calculate cosmological perturbations in dark energy models consisting of a scalar field interacting with dark matter via energy and momentum exchanges. Focusing on three well-known models of quintessence and three common types of dark-sector interactions, we calculate the matter and dark energy power spectra as well as the Integrated Sachs-Wolfe (ISW) effect in these models. We show how the presence of dark-sector interactions can produce a large-scale enhancement in the matter power spectrum and a boost in the low multipoles of the cosmic microwave background anisotropies. Nevertheless, we find these enhancements to be much more subtle than those found by previous authors who model dark energy using simple ansatz for the equation of state. We also address issues of instabilities and emphasise the importance of momentum exchanges in the dark sector.

24 pages, 9 figures. Accepted for publication in JCAP

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• Interacting Dark Energy -- constraints and degeneracies
• Cosmological constraints on interacting dark energy with redshift-space distortion after Planck data
• Testing coupled dark energy with large scale structure observation
• Coupled dark energy with perturbed Hubble expansion rate
• Cosmological constraints on coupled dark energy
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• Interacting Scalar fields: Dark matter and early dark energy
• Degeneracy between primordial non-Gaussianity and interaction in the dark sector