We explore a chameleon type of interacting dark matter–dark energy scenario in which a scalar field adiabatically traces the minimum of an effective potential sourced by the dark matter density .
We discuss extensively the effect of this coupling on cosmological observables , especially the parameter degeneracies expected to arise between the model parameters and other cosmological parameters , and then test the model against observations of the cosmic microwave background ( CMB ) anisotropies and other cosmological probes .
We find that the chameleon parameters \alpha and \beta , which determine respectively the slope of the scalar field potential and the dark matter–dark energy coupling strength , can be constrained to \alpha < 0.17 and \beta < 0.19 using CMB data alone .
The latter parameter in particular is constrained only by the late Integrated Sachs–Wolfe effect .
Adding measurements of the local Hubble expansion rate H _ { 0 } tightens the bound on \alpha by a factor of two , although this apparent improvement is arguably an artefact of the tension between the local measurement and the H _ { 0 } value inferred from Planck data in the minimal \Lambda CDM model .
The same argument also precludes chameleon models from mimicking a dark radiation component , despite a passing similarity between the two scenarios in that they both delay the epoch of matter–radiation equality .
Based on the derived parameter constraints , we discuss possible signatures of the model for ongoing and future large-scale structure surveys .