  Using holographic models where chiral symmetry is broken through IR b.c.'s,
we determine a novel set of relations between QCD matrix elements. In
particular, we find that the amplitudes of the three processes pi pi->pi pi,
gamma gamma->pi pi and gamma->pi pi pi involve a single scalar function h(Q^2)
given by a suitable 5D integral of the EoM Green's function. In a
phenomenological analysis of gamma gamma->pi pi we find an overall agreement
with the experimental cross section for a broad range of energy. Moreover, the
polarizabilities at low energies show a fair agreement between the holographic
approach, previous computations and experiment.
