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.
