The effect of composite resonances on Higgs decay into two photons

In scenarios of strongly coupled electroweak symmetry breaking,
heavy composite particles of different spin and parity may arise and cause
observable effects on signals that appear at loop levels. The recently observed process of Higgs to $\gamma \gamma$ at the LHC is one of such signals. We study the new constraints that
are imposed on composite models from $H\to \gamma\gamma$, together with the existing constraints from the high precision electroweak tests. We use an effective chiral Lagrangian to
describe the effective theory that contains the Standard Model spectrum and the extra composites
below the electroweak scale.
Considering the effective theory cutoff at $\Lambda = 4\pi v \sim 3 $ TeV, consistency with
the $T$ and $S$ parameters and the newly observed $H\to \gamma
\gamma$ can be found for a rather restricted range of masses of vector and axial-vector composites from $1.5$ TeV to $1.7$ TeV and $1.8$ TeV to $1.9$ TeV, respectively, and only
provided a non-standard kinetic mixing between the $W^{3}$ and $B^{0}$ fields is
included.