Screening Mechanism and Late-time Cosmology: Role of a Chameleon-Brans-Dicke Scalar Field

TL;DR

This paper explores how a scalar field in Brans-Dicke theory, with chameleon-like properties, can explain late-time cosmic acceleration while satisfying local gravity tests, supported by observational data.

Contribution

It introduces a scalar field with density-dependent mass in Brans-Dicke theory that can drive cosmic acceleration and pass local tests, a novel approach in scalar-tensor cosmology.

Findings

Scalar field can evade local tests via chameleon mechanism.

Observational data favor a mild scalar-matter interaction.

Model consistent with supernova, Hubble, and BAO data.

Abstract

We discuss a way in which the geometric scalar field in a Brans-Dicke theory can evade local astronomical tests and act as a driver of the late-time cosmic acceleration. This requires a self-interaction of the Brans-Dicke scalar as well as an interaction with ordinary matter. The scalar field in this construct acquires a density-dependent effective mass much like a Chameleon field. We discuss the viability of this setup in the context of the Equivalence Principle, Fifth Force, and Solar System tests. The cosmological consistency is adjudged in comparison with observational data from recalibrated light curves of type Ia supernova (JLA), the Hubble parameter measurements (OHD), and the Baryon Acoustic Oscillation (BAO). We deduct that the astrophysical constraints indeed favor the existence of a mild scalar-matter interaction in the Jordan Frame.