Tackling problems on Hadron Physics using effevtive field theories

Abstract

Resumo em Inglês As a consequence of the non-perturbative character of QCD in the intermediate energy region, the use of effective field theories to study hadron systems at those energies have become a very powerful tool nowadays. The strategy consists of using Lagrangians which implement the relevant symmetries for the system and solve the Bethe-Salpeter equation (two hadron system) or the Faddeev equations (three hadron interaction). In this way, the scattering matrix T is determined to implement unitarity in coupled channels through the summation of all the Feynman diagrams contributing to the process under study. Once the T matrix is obtained, observables as cross-sections, scattering length, decay widths, invariant mass distributions, etc., can be calculated. Within this method, we pretend to study several systems made of two and three hadrons in which states with exotic properties have been observed experimentally at facilities like Belle, BES, J-PARC, etc. Some examples are the Zc states, and those labelled as X, Y. All of them seem to have a different nature than the quark structure expected in the standard quark model. Our study will shed light on the properties and nature of these states, and cross-sections and other observables can be determined and compared with experimental data. The extension of the method to a finite volume is also very useful since we can compare our results with those of lattice QCD studies and our results can be used as a guide for future lattice studies analyzing the properties of such hadrons. (AU)