标题： 轻夸克强子的西格玛项 显示英文标题

标题： Sigma Terms of Light-Quark Hadrons

摘要： 强子质量对当前夸克质量的依赖性计算有助于利用观测数据来限制自然界基本参数的变化。 一个强子的sigma项是对这种依赖性的度量。 通过使用Dyson-Schwinger方程的彩虹阶梯截断，用π介子的显式计算展示了强子的sigma项与Feynman-Hellmann定理之间的联系：在手征极限附近，sigma_pi = m_pi/2。 这种截断也为sigma_rho提供了合理的估计，因为ρ介子质量的两个主要自能校正对其sigma_rho贡献几乎完全抵消。 然而，对于ω介子，这种截断不够准确，因为ω -> ρ + π的自能贡献会放大sigma_ω约25%。 求解描述核子和Δ粒子作为禁闭夸克和非点状二夸克组成的协变Faddeev方程，以获得核子和Δ粒子质量对当前夸克质量的依赖性，并由此得到sigma_N和sigma_Delta。 这个“夸克内核”部分由“π云”贡献增强，该贡献为正值。 分析得出sigma_N ≈ 60 MeV 和 sigma_Delta ≈ 50 MeV。 显示英文摘要

摘要： A calculation of the current-quark mass dependence of hadron masses can help in using observational data to place constraints on the variation of nature's fundamental parameters. A hadron's sigma-term is a measure of this dependence. The connection between a hadron's sigma-term and the Feynman-Hellmann theorem is illustrated with an explicit calculation for the pion using a rainbow-ladder truncation of the Dyson-Schwinger equations: in the vicinity of the chiral limit sigma_pi = m_pi/2. This truncation also provides a decent estimate of sigma_rho because the two dominant self-energy corrections to the rho-meson's mass largely cancel in their contribution to sigma_rho. The truncation is less accurate for the omega, however, because there is little to compete with an omega->rho+pi self-energy contribution that magnifies the value of sigma_omega by ~25%. A Poincare' covariant Faddeev equation, which describes baryons as composites of confined-quarks and -nonpointlike-diquarks, is solved to obtain the current-quark mass dependence of the masses of the nucleon and Delta, and thereby sigma_N and sigma_Delta. This "quark-core" piece is augmented by the "pion cloud" contribution, which is positive. The analysis yields sigma_N~60MeV and sigma_Delta~50MeV.