Quantum effects and stability of chameleon cosmology

TL;DR

This paper investigates how quantum effects influence the stability of chameleon scalar fields in cosmology, revealing potential instabilities due to conformal anomalies especially in strong gravity regions.

Contribution

It demonstrates that matter quantum effects induce conformal anomalies in chameleon cosmology, leading to higher derivative terms and potential instabilities in the scalar field equations.

Findings

Quantum effects produce conformal anomalies in chameleon fields.

Higher derivative terms can cause instabilities in strong gravity regions.

Instabilities are negligible at small curvature but significant in strong gravitational fields.

Abstract

One possibility to explain the current accelerated expansion of the universe may be related with the presence of cosmologically evolving scalar whose mass depends on the local matter density (chameleon cosmology). We point out that matter quantum effects in such scalar-tensor theory produce the chameleon scalar field dependent conformal anomaly. Such conformal anomaly adds higher derivative terms to chameleon field equation of motion. As a result, the principal possibility for instabilities appears. These instabilities seem to be irrelevant at small curvature but may become dangerous in the regions where gravitational field is strong.