Detecting Chameleons: The Astronomical Polarization Produced by Chameleon-like Scalar Fields

TL;DR

This paper investigates how chameleon-like scalar fields coupled to photons can produce detectable polarization signals in astrophysical light, offering new constraints and potential evidence for such fields.

Contribution

It provides numerical and analytical models of polarization induced by chameleon-like scalar fields and significantly improves constraints on their coupling parameters.

Findings

Improved constraints on chameleon-photon coupling by over two orders of magnitude.

Predicted distinctive circular polarization as a smoking gun for chameleon detection.

Tentative statistical evidence of a chameleon-like scalar field from galactic starlight polarization.

Abstract

We show that a coupling between chameleon-like scalar fields and photons induces linear and circular polarization in the light from astrophysical sources. In this context chameleon-like scalar fields includes those of the Olive-Pospelov (OP) model describing a varying fine structure constant. We determine the form of this polarization numerically and give analytic expressions in two useful limits. By comparing the predicted signal with current observations we are able to improve the constraints on the chameleon-photon coupling and the coupling in the OP model by over two orders of magnitude. It is argued that, if observed, the distinctive form of the chameleon induced circular polarization would represent a smoking gun for the presence of a chameleon. We also report a tentative statistical detection of a chameleon-like scalar field from observations of starlight polarization in our galaxy.