Impact of charge symmetry breaking on gluon and sea quark distributions in the pion and kaon.

In this exploratory study, I present, for the first time, the implications of the charge symmetry breaking (CSB) that arise from the u and d quark-mass differences on gluon and sea quark distribution functions of the pion and kaon in the framework of the Nambu–Jona-Lasino (NJL) model, which is a quark-level chiral effective theory of QCD, with the help of the proper-time regularization scheme to simulate color confinement of QCD. From the analysis, one finds that the charge symmetry (CS) gluon distribution for the pion has a good agreement with the prediction results obtained from the recent lattice QCD simulation and JAM global fit QCD analysis at a higher scale of Q 2 = 5 GeV2. The size of the CSB effects on gluon and sea quark distributions for the pion with the realistic ratios of m u / m d = 0. 5 at Q 2 = 5 GeV2 are, respectively, estimated by 1.3% and 2.0% at x ≃ 1 in comparison with those for m u / m d = 1. 0 , while those for the kaon are approximately about 0.3% and 0.5% at x ≃ 1 , respectively. A remarkable result is found that the CSB effects on gluon distribution for the kaon are smaller than that for the pion, which has a similar prediction result as that for the CS case. [ABSTRACT FROM AUTHOR]