Wavefunction-Independent Relations between the Nucleon Axial-Coupling g_A and the Nucleon Magnetic Moments

Stanley J. Brodsky; Felix Schlumpf

doi:10.1016/0370-2693(94)90525-8

paper

Wavefunction-Independent Relations between the Nucleon Axial-Coupling g_A and the Nucleon Magnetic Moments

arXiv:hep-ph/9402214 · doi:10.1016/0370-2693(94)90525-8

Abstract

We calculate the proton's magnetic moment $μ_{p}$ and its axial-vector coupling $g_{A}$ as a function of its Dirac radius $R_{1}$ using a relativisitic three-quark model formulated on the light-cone. The relationship between $μ_{p}$ and $g_{A}$ is found to be independent of the assumed form of the light-cone wavefunction. At the physical radius $R_{1} = 0.76$ fm, one obtains the experimental values for both $μ_{p}$ and $g_{A}$ , and the helicity carried by the valence $u$ and $d$ quarks are each reduced by a factor $≃ 0.75$ relative to their non-relativistic values. At large proton radius, $μ_{p}$ and $g_{A}$ are given by the usual non-relativistic formulae. At small radius, $μ_{p}$ becomes equal to the Dirac moment, as demanded by the Drell-Hearn-Gerasimov sum rule. In addition, as $R_{1} \to 0,$ the constituent quark helicities become completely disoriented and $g_{A} \to 0$ .

17 pages, RevTeX, 4 uuencoded figures, SLAC-PUB-6431

Wavefunction-Independent Relations between the Nucleon Axial-Coupling g_A and the Nucleon Magnetic Moments

Abstract

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