Richard F. Lebed

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A new measurement of the Ξ mass verifies the accuracy of the ColemanGlashow relation at the level predicted by the 1/Nc expansion. Values for other baryon isospin mass splittings are updated, and continue to agree with the 1/Nc hierarchy. 11.15.Pg, 14.20.-c,13.40.Dk Typeset using REVTEX ejenkins@ucsd.edu lebed@jlab.org The recent measurement of the Ξ mass(More)
Jurčo, Möller, Schraml, Schupp, and Wess have shown how to construct noncommutative SU(N) gauge theories from a consistency relation. Within this framework, we present the Feynman rules for noncommutative QCD and compute explicitly the most dangerous Lorentz-violating operator generated through radiative corrections. We find that interesting effects appear(More)
These lectures are designed to introduce the methods and results of large Nc QCD in a presentation intended for nuclear and particle physicists alike. Beginning with definitions and motivations of the approach, we demonstrate that all quark and gluon Feynman diagrams are organized into classes based on powers of 1/Nc. We then show that this result can be(More)
The "true microonium" (micro+micro-) and "true tauonium" (tau+tau-) bound states are not only the heaviest, but also the most compact pure QED systems. The rapid weak decay of the tau makes the observation of true tauonium difficult. However, as we show, the production and study of true microonium is possible at modern electron-positron colliders.
We use both old and new theoretical developments in QCD dispersion relation constraints on the scalar form factor in the decay K → πlνl to obtain constraints on the strange quark mass. The perturbative QCD side of the calculation incorporates up to four-loop corrections, while the hadronic side uses a recently developed parameterization constructed(More)
We present a model of fermion masses based on a minimal, non-Abelian discrete symmetry that reproduces the Yukawa matrices usually associated with U(2) theories of flavor. Mass and mixing angle relations that follow from the simple form of the quark and charged lepton Yukawa textures are therefore common to both theories. We show that the differing(More)
We compute and tabulate the Clesbsch–Gordan coefficients of the SU(6) ⊃ SU(3) × SU(2) product 56 ⊗ 56, which are relevant to the nonrelativistic spin-flavor symmetry of the lightest baryons. Under the assumption that the largest representation in this product, the 2695, gives rise to operators in a chiral expansion that produce numerically small effects, we(More)