Search for chameleons with CAST

TL;DR

This study used the CERN Axion Solar Telescope to search for solar chameleons, setting new limits on their coupling to photons, despite not detecting any excess signal.

Contribution

First experimental search for solar chameleons using CAST, establishing new constraints on their photon coupling in a novel dark energy research approach.

Findings

No excess above background observed.

Set 95% C.L. limit on chameleon-photon coupling $eta_{ m \

Set a limit of $eta_{ m \

Abstract

In this work we present a search for (solar) chameleons with the CERN Axion Solar Telescope (CAST). This novel experimental technique, in the field of dark energy research, exploits both the chameleon coupling to matter ($\beta_{\rm m}$) and to photons ($\beta_{\gamma}$) via the Primakoff effect. By reducing the X-ray detection energy threshold used for axions from 1$\,$keV to 400$\,$eV CAST became sensitive to the converted solar chameleon spectrum which peaks around 600$\,$eV. Even though we have not observed any excess above background, we can provide a 95% C.L. limit for the coupling strength of chameleons to photons of $\beta_{\gamma}\!\lesssim\!10^{11}$ for $1<\beta_{\rm m}<10^6$.