We analyze the PVLAS results using a chameleon field whose properties depend on the environment. We find that, assuming a runaway bare potential $V(\varphi )$ and a universal coupling to matter, the chameleon potential is such that the scalar field can act as dark energy. Moreover, the chameleon-field model is compatible with the CERN Axion Solar Telescope results, fifth-force experiments, and cosmology.

• Received 26 March 2007

DOI:https://doi.org/10.1103/PhysRevLett.99.121103