Meson-baryon Scattering In Chiral Perturbation Theory

As it is well known,quantum chromodynamics?QCD?is the theory of the strong interaction.But it is very difficult to study low-energy hadronic processes by using the theory directly because of its asymptotic freedom,color confinement and the other property.However,chiral perturbation theory?ChPT?is treated as the effective field theory of QCD,it is a model independent method.Thus,in this thesis,we study the pseudoscalar meson octet-baryon scattering in heavy baryon chiral perturbation theory?HB?PT?and extend the application of hadron physics at the low energy with HB?PT.It is necessary to calculate partial-wave phase shifts about a scattering process because the complete information in the physical region is contained in partial-wave phase shifts.First,we calculate the amplitudes of kaon-nucleon?KN?and antikaon-nucleon????N?scattering to one-loop order in HB?PT.Then,we deter-mine the low-energy constants?LECs?from the high-order Lagrangian by fitting to the empirical partial-wave phase shifts of KN scattering.We predict the phase shifts of???N scattering by use of these LECs,and obtain a reasonable result.We also predict the scattering lentghs of KN and???N,which turn out to be in agreement with the empirical values within errors except for the isospin-0???N scattering length that is dominated by the??1405?resonance.After achieving some success for calculating the KN and???N scattering,we continue to calculate amplitudes of pseudoscalar meson octet-baryon scattering to one-loop order in HB?PT.The low-energy constants in these amplitudes are determined by fitting to the empirical phase shifts of?N and KN scattering.For improving the fits of?N scattering,we consider the counterterm contributions to the?N channels at the third order.Then we predict phase shifts and scattering lengths for the other channels by using these low-energy constants.We obtain the strong phase shit difference of??scattering at the?mass,?8.8±0.2?degrees,in agreement with experimental results.We find that the phase shifts in the S₀₁????,S₀₁?K??,S₀₁????N?and S₁₁??????waves are so strong that resonances may be gen-erated dynamically in all these channels.In fact,the S₀₁????,S₀₁?K??,S₀₁????N?and S₁₁??????waves are related to the??1405?,??1670?,??1405?and??1690?,respectively.We also predict the scattering lengths and make comparisons with the results obtained from the method of covariant infrared regularization.We find that those results are not better than our predictions.In both approaches the higher order contributions need to be calculated.We also discuss the issue of convergence in detail and find that the good convergence is obtained possibly when the fourth order contributions are included at least.