Isospin Symmetry Breaking in the Chiral Quark Model

TL;DR

This paper investigates isospin symmetry breaking in nucleon quark distributions within the chiral quark model, analyzing its impact on the Gottfried sum rule and NuTeV anomaly, and finds flavor asymmetry as the main contributor.

Contribution

It provides a detailed analysis of isospin symmetry breaking effects on quark distributions, emphasizing the dominance of flavor asymmetry and its implications for sum rules and anomalies.

Findings

Flavor asymmetry mainly causes Gottfried sum rule violation.

Isospin symmetry breaking cannot resolve the NuTeV anomaly.

Results align with established quark distribution parametrizations.

Abstract

We discuss the isospin symmetry breaking (ISB) of the valence- and sea-quark distributions between the proton and the neutron in the framework of the chiral quark model. We assume that isospin symmetry breaking is the result of mass differences between isospin multiplets and then analyze the effects of isospin symmetry breaking on the Gottfried sum rule and the NuTeV anomaly. We show that, although both flavor asymmetry in the nucleon sea and the ISB between the proton and the neutron can lead to the violation of the Gottfried sum rule, the main contribution is from the flavor asymmetry in the framework of the chiral quark model. We also find that the correction to the NuTeV anomaly is in an opposite direction, so the NuTeV anomaly cannot be removed by isospin symmetry breaking in the chiral quark model. It is remarkable that our results of ISB for both valence- and sea-quark distributions are consistent with the Martin-Roberts-Stirling-Thorne parametrization of quark distributions.