Quark Contributions to Baryon Magnetic Moments in Full, Quenched and Partially Quenched QCD

TL;DR

This paper investigates how quark contributions affect baryon magnetic moments across full, quenched, and partially-quenched QCD, revealing detailed nonanalytic behaviors and testing the structure of baryons and chiral effects.

Contribution

It introduces an efficient diagrammatic approach to separate quark-sector contributions in different QCD approximations, accounting for SU(3) symmetry violations and providing testable predictions.

Findings

Valence u-quark contribution reveals nonanalytic behavior in full QCD.

Quenched approximation artifacts are observable in the u quark of Sigma^+.

Method enables detailed analysis of quark-sector contributions in various QCD regimes.

Abstract

The chiral nonanalytic behaviour of quark-flavor contributions to the magnetic moments of octet baryons are determined in full, quenched and partially-quenched QCD, using an intuitive and efficient diagrammatic formulation of quenched and partially-quenched chiral perturbation theory. The technique provides a separation of quark-sector magnetic-moment contributions into direct sea-quark loop, valence-quark, indirect sea-quark loop and quenched valence contributions, the latter being the conventional view of the quenched approximation. Both meson and baryon mass violations of SU(3)-flavor symmetry are accounted for. Following a comprehensive examination of the individual quark-sector contributions to octet baryon magnetic moments, numerous opportunities to observe and test the underlying structure of baryons and the nature of chiral nonanalytic behavior in QCD and its quenched variants are discussed. In particular, the valence u-quark contribution to the proton magnetic moment provides the optimal opportunity to directly view nonanalytic behavior associated with the meson cloud of full QCD and the quenched meson cloud of quenched QCD. The u quark in Sigma^+ provides the best opportunity to display the artifacts of the quenched approximation.