Vacuum Polarization in Nucleon Structure
We draw analogies between the shell model and the quark model and also between the many body theory and the lattice gauge theory. We then report results of our lattice calculations on the πN σ term and the flavor-singlet axial charge of the nucleon in the framework of quenched QCD. The disconnected insertions, or vacuum polarizations, which involve contributions from the sea quarks are evaluated with the stochastic estimator with the Z 2 noise which yields minimum variances. We find the sea-quark contribution to the πN sigma term to be ~ 1/2 – 1/4 of that of the dynamical fermion calculation. Whereas, the sea-quark contribution to the flavor-singlet g A is negative and large enough to cancel the valence (connected insertion) contribution substantially to resolve the “proton spin crisis”.
KeywordsQuark Mass Quark Model Vacuum Polarization Lattice Gauge Theory Body Theory
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