Constraints on chameleons and axion-like particles from the GammeV   experiment
  We present the most recent results of both aspects of the GammeV experiment. The first aspect is a search for axion-like particles using a variable baseline, "light-shining-through-a-wall" technique. This search excludes the particle interpretation of the PVLAS signal with high confidence. The second aspect of the GammeV experiment is a search for chameleon particles, scalar particles which may be responsible for the dark energy of the universe. This is accomplished by looking for a characteristic afterglow signature from a "particle-in-a-jar" experiment whereby chameleon particles become trapped in a region with a high magnetic field and slowly decay into detectable photons. This is the first use of this experimental technique to probe for these particles. We place interesting limits on a limited range of general chameleon models. These limits are complimentary to other experiments, such as torsion pendulum experiments, which probe for forces that would result from new scalar particles. 
Jason H. Steffen (for the GammeV collaboration)