Studies Of Light Mesons' Parton Distribution Amplitudes

A symmetry-preserving truncation("rainbow-ladder" truncation)of the two-body bound-state problem in relativistic quantum field theory is used to compute the leading-twist parton distribution amplitudes(PDAs)for the ground and the first radial excita-tions of the light mesons.In the calculations,the famous "Qin-Chang" model is used.This model reveals that in the infrared region,the gluon propagator has an signifi-cant enhancement;while in the ultraviolet region,it has the same behavior as which in one-loop perturbative QCD.Hence,during calculating the quark Dyson-Schwinger equation,an subtract scheme is adopted,and so as "Pauli-Villar" regularization.The mass function of the quark propagator also has a significant enhancement in the in-frared region,which exhibit the effect of chiral dynamical symmetry breaking.For the 7r-and K-mesons,in common with ground states in these channels,the PDAs are found to be dilated with respect to the relevant conformal-limit form and skewed toward the heavier valence-quark in asymmetric systems.In addition,the PDAs of radially-excited pseudoscalar mesons are not positive definite,owing to the fact that dynamical chiral symmetry breaking(DCSB)forces the leptonic decay con-stant of such states to vanish in the chiral limit.These results highlight that DCSB is expressed visibly in every pseudoscalar meson constituted from light-quarks.Hence,so long as its impact is empirically evident in the pseudoscalar members of a given spectrum level,it is unlikely that chiral symmetry is restored in any of the hadrons that populate this level.Owing to the fact that the scale-independent leptonic decay constant of a scalar meson constituted from equal-mass valence-constituents vanishes,it is found that the PDA of a given scalar system possesses one more zero than that of an analogous vector meson.Consequently,whereas the mean light-front relative momentum of the valence-constituents within a vector meson is zero,that within a scalar meson is large,an out-come which hints at a greater role for light-front angular momentum in systems classi-fied as P-wave in quantum mechanical models.Values for the scale-dependent decay constants of ground-state scalar and vector systems are a by-product of this analysis,and they turn out to be roughly equal,viz.(?)0.2 GeV at an hadronic scale.In addi-tion,it is confirmed that the dilation characterising ground-state PDAs is manifest in the PDAs of radial excitations too.The impact of SU(3)-flavour symmetry breaking is also considered.When compared with pseudoscalar states,it is a little stronger in scalar systems,but the size is nevertheless determined by the flavour-dependence of dynamical chiral symmetry breaking and the PDAs are still skewed toward the heavier valence-quark in asymmetric systems.