Photon Light-Cone Wave Functions And QCD Sum Rules

The eight off-shell light-cone photon wavefunctions corresponding to chiral-odd and chiral-even up to twist-four and the corresponding coupling constants are system-atically investigated in framework of the low-energy effective theory of quantum chro-modynamics; and in meanwhile, the vector meson coupling constants in the processes of a vector meson decaying into a scalar meson and a photon are calculated by using QCD light-cone sum rules.First, according to the principle of the Lorentz covariance, the transition matrix elements from an off-shell photon state to the vacuum are decomposed into the eight light-cone photon distribution amplitudes, in which only two transversal wavefunc-tions survive in the on-shell limit. After separating them through the corresponding projection operators, the various individual photon DA multiplied by its corresponding coupling constant is universally expressed in terms of the correlation functions. Using the spectral representation of a general quark propagator, the universal expressions for all the photon DAs times the coupling constants in terms of these spectral density functions are obtained.Further, in order to consider the non-perturbative effects of QCD, we have been choosing to work in the framework of the QCD low-energy effective theory. We have introduced a usual pole form for the effective quark propagator in that theory, and worked out the analytic expressions of the corresponding spectral density function-s, which obey the well-known constraints for the fermionic spectral densities indeed. Using these analytic forms, the analytic expressions of the eight photon DAs and the corresponding coupling constants are obtained.Imputing the experienced standard parameters in the QCD low-energy effective theory, we have carried out the numerical simulation, and the numerical results (in-cluding the corresponding curves for the wavefunctions versus the quark momentum fraction u) of all wavefunctions (including the pure twist-3part of the photon wavefunc-tions hγ(t),hγ||(s),gγ⊥(v) and gγ⊥(α)) are given out. All the coupling constants are calculated by using the normalization conditions, and both the analytical and numerical relationship between the couplings and the photon momentum squared P2are given. At last, the obtained wavefunctions are expanded in Gegenbauer polynomials, the corresponding expanding coefficients are listed.After completing the calculation of the light-cone photon wavefunctions and their coupling constants, the processes in any one of which a vector meson is decaying into a scalar meson and a photon are studied by using our numerical results for the photon wavefunctions. The corresponding coupling constants for such processes are calculated by using QCD light-cone sum rules.Finally, we have made our conclusions and compared our results with the others in literatures, and in meanwhile, given a significant discussion and further outlook for the application of our obtained photon wavefunctions.