How CMB and large-scale structure constrain chameleon interacting dark energy

Abstract

We explore a chameleon type of interacting dark matter-dark energy scenario in which a scalar field adiabatically traces the minimum of an eff ective potential sourced by the dark matter density. We discuss extensively the effect of this coupling on cosmological observables, especially the parameter degeneracies expec ted to arise between the model pa- rameters and other cosmological parameters, and then test t he model against observations of the cosmic microwave background (CMB) anisotropies and o ther cosmological probes. We find that the chameleon parameters α and β , which determine respectively the slope of the scalar field potential and the dark matter-dark energy coupl ing strength, can be constrained to α < 0 . 17 and β < 0 . 19 using CMB data and measurements of baryon acoustic oscill ations. The latter parameter in particular is constrained only by th e late Integrated Sachs-Wolfe effect. Adding measurements of the local Hubble expansion ra te H 0 tightens the bound on α by a factor of two, although this apparent improvement is arg uably an artefact of the tension between the local measurement and the H 0 value inferred from Planck data in the minimal ΛCDM model. The same argument also precludes chameleon mode ls 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 d erived parameter constraints, we discuss possible signatures of the model for ongoing and fut ure large-scale structure surveys.