  We explore the collider relevance of a charge-radius coupling among light
mesons in composite Higgs models. In particular, we focus of a coupling of the
photon to the composite Higgs and a composite singlet, arising from isospin
violation in the underlying theory. This coupling offers a deep probe of the
composite nature of the Higgs mechanism, being sensitive to the electromagnetic
and weak isospin structure of its constituents. The main collider effect
consists in the production of the Higgs boson in association with a light
composite pseudo-scalar. We present an exploratory cut-and-count analysis at
hadron colliders, like the LHC, showing that an efficient background
suppression can be achieved. More sophisticated techniques, however, are
necessary to select a sufficient number of signal events, due to the small
production rates. This justifies further investigation of this channel, which
is highly complementary to other searches for compositeness in the Higgs
sector.
