Oset, E.Marco, E.Nacher, J. C.Oller, J. A.Peláez Sagredo, José RamónRamos Ruiz, AmparoToki, H.2023-06-202023-06-2020000146-641010.1016/S0146-6410(00)00073-9https://hdl.handle.net/20.500.14352/59877©Elsevier Science BV. Erice School on Electromagnetic Probes and the Structure of Hadrons and Nuclei (1999. Erice, Italia). This work is partly supported by DGICYT, contract number PB 96-0753By means of a coupled channel non-perturbative unitary approach, it is possible to extend the strong constrains of Chiral Perturbation Theory to higher energies. In particular, it is possible to reproduce the lowest lying resonances in mesonmeson scattering up to 1.2 GeV using the parameters of the O(p²) and O ( p^ 4 ) Chiral Lagrangian. The meson baryon sector can also be tackled along similar lines. We report on an update of these results showing some examples of photon induced reactions where the techniques have been recently applied.engjournal articlehttp://dx.doi.org/10.1016/S0146-6410(00)00073-9http://www.sciencedirect.comhttp://arxiv.org/abs/nucl-th/9911040open access51-73Perturbation-theoryOne-loopScalar mesonsForm-factorsScatteringUnitarizationLagrangiansAmplitudesChannelsSymmetryFísica-Modelos matemáticosFísica matemática