Light-cone Distribution Amplitudes And Their Applications In Nonperturbative QCD

Light-cone distribution amplitudes of hadrons, which are the fundamental parameters in hard exclusive processes and the light-cone QCD sum rules, contain information of the hadron structure and play an essential role in applications of the light-cone QCD sum rules. The main aims of this thesis are to examine the distribution amplitudes of the octet baryons, and to investigate their applications.The light-cone distribution amplitudes ofΣ±,ΛandΞbaryons are presented up to twist 6. We first give the general definitions of the octet baryon distribution amplitudes in the SU(3) flavor symmetry limit. The number of the independent distribution amplitudes is reduced with the aid of some symmetry relationships. By considering the conformal symmetry of the massless QCD Lagrangian, the distribution amplitudes are expanded by the conformal partial waves to the leading order of the conformal spin accuracy. With the help of the equation of motion, the coefficients of the conformal expansion are related to some other nonperturbative parameters, which are determined in the framework of QCD sum rules. We then give the explicit expressions of the distribution amplitudes ofΣ±,ΛandΞ. In the calculation, we take into account contributions from SU(3) flavor symmetry breaking effects as corrections.The distribution amplitudes obtained in this thesis make it possible to study some parameters and physical processes related to the baryons with the light-cone QCD sum rules. As applications, we calculate the electromagnetic form factors ofΣ±, A andΞbaryons in the intermediate momentum transfer. The magnetic moments of the baryons are estimated from the assumption that the magnetic form factors can be fitted by the dipole formula. We also predict the decay widths and branching ratios of the semileptonic decay modesΛc→Λl+vl andΞc→Ξe+ve with the light-cone sum rules of the related weak transition form factors, as well as exclusive rare decay processΛb→Λγ.In addition, we recalculate the same electromagnetic form factors and the semilep-tonic decay modes with an alternative interpolating currents. Our results show that the choice of the interpolating currents does not lead to obvious difference but for the A baryon, while the Ioffe-type currents give more reliable predictions for the semileptonic decay processes.