| The interactions between hadrons and the properties and internal structure ofhadrons are the most important topics in the field of hadron physics. The chiralunitary approach (ChUA) succeeded in reproducing the meson-meson scattering data.Meanwhile theσ,f0(980),a0(980) andκstates can be dynamically generated. In thisthesis, under the framework of the chiral model and the chiral unitary approach, thecoupled-channel Bethe-Salpeter (BS) equation is used to generally study the everysectors of the interactions between the octet of light pseudoscalar mesons and the octetof 21+ baryons, with the aim at finding the physical states in strong interaction andexplaining the structure of them. The scattering amplitudes of every channel, whichare drawn from the lowest order meson-baryon chiral Lagrangians, are employed asthe kernel potentials of a set of coupled-channel BS equations to resum an infinitenumber of s channel loops, and the obtained amplitude satisfies the unitary relationexactly. The meson decay constants are taken their experimental data for di?erentchannels. The free parameters in this method are the regularization constants fordi?erent channels.Both of the dimensional regularization and the 3-momentum cut-o? regularizationmethod are used to deal with the divergence in the one loop integral. The e?ects ofdi?erent regularization methods to the numerical result are investigated. It is showedthat there is no di?erences using two of them in the results of theπΣscattering inS = ?1 sector. But in theπN scattering of S = 0 sector and theπΞscattering ofS = ?2 sector, the formulas of 3-momentum cut-o? could not be used to regularize theloop integrals because using them artificial singularity appears in some channels, andin this situation the method could not be used to fit the experiments data. Thereforethe dimensional regularization method is employed for the better to treat with thedivergence of the loop integrals in our work.In the strangeness S = 0 sector of the meson-baryon scattering (πN scattering), firstly the experiments'data about the T amplitude of theπN partial wave is taken tofix the free parameters in the fitting procedure. And then the poles of the scatteringamplitudes are searched by the fitting parameters. In our results, the nucleon excitedstate N?(1535), is dynamically generated in isospin I = 21 section of theπN coupledchannels scattering. The obtained mass and width of N?(1535) are that M = 1.51217GeV andΓ88 MeV. After discussion, N?(1535) is considered as meson-baryonmolecules likeπN +ηN and not only a pure normal three-quarks baryon state.In the strangeness S = ?1 sector of the meson-baryon scattering (πΣscattering),we successfully produced two resonances in isospin I = 0,Λ(1405) andΛ(1670). Themass and width of them areΛ(1405) (M = 1.42899 GeV,Γ32 MeV) andΛ(1670)(M = 1.67276 GeV,Γ52 MeV), which are well consistent with the experiments.Besides, in isospin I = 1 section of theπΣcoupled channels scattering, one pole isfound in the forth Riemann sheet, which is (1.54334+0.273103 i) GeV and is accordingwith the resonanceΣ(1620). These indicate that the baryon resonances of strangenessS = 1,Λ(1405),Λ(1670) andΣ(1620) are of the component meson-baryon molecules.In the strangeness S = ?2 sector of the meson-baryon scattering (πΞscattering),the studied results of theπΞcoupled channels scattering in isospin I = 21 section in-dicates that a resonance appears in 1.5 GeV of the energy axial, which not only foundin theπΞmass distribution but also in the poles finding. There are two poles in thesecond Riemann sheet that may be have some sense, (1.48622 + 0.00362948 i) GeVand (1.51927 ? 0.312818 i) GeV. The two poles should be considered as resonances.The first one may be a narrow width resonance of 7 MeV the mass of which is 1.48622GeV, and the other one a large width resonance of 620 MeV, mass as 1.51927 GeV.But they are not listed in Particle Data Group.
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