Strong coupling expansions in pure lattice gauge theory mixed actions: Carles Ayala and Marià Baig. Grup de Física Teòrica, Universitat Autònoma de Barcelona, 08193 Bellaterra, Barcelona, Spain

Abstract

A determination of spin-orbit splitting in N and Λ using the QCD sum rule technique of Shifman, Vainshtein, and Zakharov is presented. The QCD sum rules coupling to JP = 12− nucleons, first considered by Belyaev and Ioffe are shown to provide a consistent description of N12−(1535). The QCD sum rules coupling to the low-lying Δ12+, Λ12−, and Λ32−, are presented as these sum rules have not been previously considered in the literature. The non-perturbative calculations of spin-orbit splitting and odd parity excitation energies in the low-lying states of N and Λ are in agreement with experimental data. This is in contrast to conventional quark models. The large spin-orbit splitting in Λ resonances arises without invoking coupling to the KN scattering channel. The reduction of the strange quark condensate relative to the u or d quark condensate acts to increase the spin-orbit splitting in the low-lying Λ resonances. The results do not exclude coupling of Λ(1405) to the KN channel provided any additional spin-orbit splitting arising from the coupling is of the order of 30 MeV. Finally the Δ12+ sum rules cast doubt on the existence of the unconfirmed (one ∗) Δ12+(1550) resonance.