Combined cosmological and solar system constraints on chameleon mechanism

TL;DR

This paper investigates the chameleon mechanism in scalar-tensor gravity theories, showing it cannot simultaneously explain cosmic acceleration and satisfy solar system constraints within the studied model.

Contribution

It provides a combined analysis of cosmological and solar system data to constrain the chameleon mechanism parameters, highlighting incompatibility with cosmic acceleration requirements.

Findings

Chameleon mechanism cannot explain cosmic acceleration within the studied model.

Solar system constraints exclude parameter regions needed for cosmic acceleration.

Likelihood analysis rules out simultaneous viability of the mechanism for both scales.

Abstract

Chameleon mechanism appearing in massive tensor-scalar theory of gravity can effectively reduce locally the non-minimal coupling between the scalar field and matter. This mechanism is invoked to reconcile large-scale departures from general relativity (GR), supposedly accounting for cosmic acceleration, to small scales stringent constraints on GR. In this paper, we carefully investigate this framework on cosmological and solar system scales to derive combined constraints on model parameters, notably by performing a non-ambiguous derivation of observables like luminosity distance and local post-newtonian parameters. Likelihood analysis of type Ia Supernovae data and of admissible domain for the PPN parameters clearly demonstrates that chameleon mechanism cannot occur in the same region of parameters space than the one necessary to account for cosmic acceleration with the assumed Ratra-Peebles potential and exponential coupling function.