Richard F Lebed

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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 N c 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/N c. We then show that this result can be(More)
We compute the nonleptonic weak decay width of a heavy-light meson in 1+1 spacetime dimensions with a large number of QCD colors (the 't Hooft model) as a function of the heavy quark mass. In this limit, QCD is exactly soluble, and decay modes are dominated by two-particle final states. We compare the results to the tree-level partonic decay width of the(More)
We use rigorous QCD dispersion relations to derive model-independent bounds on the B → πlν, D → πlν and D → K lν form factors. These bounds are particularly restrictive when the value of the observable form factor at one or more kinematic points is assumed. With reasonable assumptions we find f B ≤ 195 MeV and that the shape of the form factor becomes(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 consider in detail the mass operator analysis for the nonstrange ℓ = 1 excited baryons in large N c QCD. We present a straightforward procedure for constructing the large N c baryon wavefunctions, and provide complete analytic expressions for the matrix elements of all the independent isosin-glet mass operators. We discuss the relationship between the(More)
We use both old and new theoretical developments in QCD dispersion relation constraints on the scalar form factor in the decay K → πℓν ℓ 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 precision corrections to dispersion relation bounds on form factors in bottom hadron semileptonic decays and analyze their effects on parameterizations derived from these bounds. We incorporate QCD two-loop and nonperturbative corrections to the two-point correlator, consider form factors whose contribution to decay rates is suppressed by lepton(More)
We present the complete flavor SU(3) decomposition of decay amplitudes for decays of the triplet (B + u , B 0 d , B 0 s) of B mesons nonleptonically into two pseudoscalar mesons. This analysis holds for arbitrarily broken SU(3) and can be used to generate amplitude relations when physical arguments permit one to neglect or relate any of the reduced(More)