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Electroweak chiral Lagrangian with a light Higgs and $γγ\to Z_L Z_L, W_L^+ W_L^-$ scattering at one loop

In these proceedings we provide a brief summary of the findings of a previous article where we have studied the photon-photon scattering into longitudinal weak bosons within the context of the electroweak chiral Lagrangian with a light Higgs, a low-energy effective field theory including a Higgs-like scalar singlet and where the electroweak would-be Goldstone bosons are non-linearly realized. We consider the relevant Lagrangian up to next-to-leading order in the chiral counting, which is explained in some detail here. We find that these amplitudes are ultraviolet finite and the relevant combinations of next-to-leading parameters ($c_γ$ and $a_1-a_2+a_3$) do not get renormalized. We propose the joined analysis of $γγ$-scattering and other photon related observables ($Γ(h\toγγ)$, $S$--parameter and the $γ^*\to W^+_LW^-_L$ and $γ^*\to hγ$ electromagnetic form-factors) in order to separate and determine each chiral parameter. Moreover, the correlations between observables provided by the NLO computations would lead to more stringent bounds on the new physics that is parametrized by means of this effective Lagrangian. We also show an explicit computation of the $γγ$--scattering up to next-to-leading order in the $SO(5)/SO(4)$ minimally composite Higgs model.