2003/06/16 by E. G. Drukarev, M. G. Ryskin, V. A. Sadovnikova +4 · 1 citation
Physics and Astronomy · #High-Energy Particle Collisions Research #Particle physics theoretical and experimental studies #Quantum Chromodynamics and Particle Interactions #hep-ph
paper · pdf · doi:10.1103/physrevd.68.054021
published as Phys.Rev. D68 (2003) 054021 · 40 pages, 3 PS figures
arxiv created 2003/06/16 · openalex publication_date 2003/09/29 · arxiv updated 2009/11/30 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/30
We calculate the expectation values of QCD operators consisting of the products of the four operators of the light quarks q\ensuremathΓXqq\ensuremathΓYq, with \ensuremathΓX,Y corresponding to the scalar, pseudoscalar, vector, pseudovector (axial), and tensor Lorentz structures, in the nucleon. All combinations of the light flavors are considered. For the evaluation we use elements of the perturbative chiral quark model (PCQM), approximating the contribution of the valence quarks by the contribution of the PCQM constituent quarks. The contribution of the sea quarks is treated by averaging over the QCD pions with the distribution of the pion field being determined by the PCQM. For quarks with the same flavor the expectation values are dominated by the contribution of the sea quarks. In the scalar case the contribution of the sea quarks is dominated by the ``disconnected terms'' where one of the pairs of the qq operators acts on the vacuum while the other one acts on the quarks of the pion. The role of the interference terms with one of the qq pairs acting on the sea quarks and the other one acting on the valence quarks increases for quarks with different flavors. The result for the scalar condensate is compared to that obtained earlier in the framework of the Nambu--Jona-Lasinio model.