Chameleon particle

Chameleon particles were proposed in 2003 by Khoury and Weltman.

In most theories, chameleons have a mass that scales as some power of the local energy density: ${\displaystyle m_{\text{eff}}\sim \rho ^{\alpha }}$, where ${\displaystyle \alpha \simeq 1}$.

Chameleons also couple to photons, allowing photons and chameleons to oscillate between each other in the presence of an external magnetic field.[3]

Chameleons can be confined in hollow containers because their mass increases rapidly as they penetrate the container wall, causing them to reflect. One strategy to search experimentally for chameleons is to direct photons into a cavity, confining the chameleons produced, and then to switch off the light source. Chameleons would be indicated by the presence of an afterglow as they decay back into photons.[4]

A number of experiments have attempted to detect chameleons along with axions.[5]

The GammeV experiment[6] is a search for axions, but has been used to look for chameleons too. It consists of a cylindrical chamber inserted in a 5 T magnetic field. The ends of the chamber are glass windows, allowing light from a laser to enter and afterglow to exit. GammeV set the limited coupling to photons in 2009.[7]

CHASE (CHameleon Afterglow SEarch) results published in November 2010,[8] improve the limits on mass by 2 orders of magnitude and 5 orders for photon coupling.

A 2014 neutron mirror measurement excluded chameleon field for values of the coupling constant ${\displaystyle \beta >5.8\times 10^{8}}$,[9] where the effective potential of the chameleon quanta is written as ${\displaystyle V_{\text{eff}}=V(\Phi )+e^{\beta \Phi /M'_{\text{P}}}\rho }$, ${\displaystyle \rho }$ being the mass density of the environment, ${\displaystyle V(\Phi )}$ the chameleon potential and ${\displaystyle M'_{\text{P}}}$ the reduced Planck mass.

The CERN Axion Solar Telescope has been suggested as a tool for detecting chameleons.[10]