The XMM Cluster Survey: Testing chameleon gravity using the profiles of clusters

Understand

The chameleon gravity model postulates the existence of a scalar field that couples with matter to mediate a fifth force.

• If it exists, this fifth force would influence the hot X-ray emitting gas filling the potential wells of galaxy clusters.
• However, it would not influence the clusters' weak lensing signal.
• Therefore, by comparing X-ray and weak lensing profiles, one can place upper limits on the strength of a fifth force.