Nucleon mass: trace anomaly and $\sigma$-terms

TL;DR

This paper explains the origin of nucleon mass, emphasizing the role of trace anomaly and gluon fields, and reviews the contributions from quark masses and Higgs mechanism through sigma-terms.

Contribution

It provides a pedagogical overview of the trace anomaly's role in nucleon mass and updates on nucleon sigma-terms related to quark mass contributions.

Findings

Trace anomaly accounts for most of the nucleon mass.

Gluon fields significantly contribute to nucleon mass.

Current status of nucleon sigma-terms is summarized.

Abstract

We give a pedagogical introduction to the origin of the mass of the nucleon. We first review the trace anomaly of the energy-momentum tensor, which generates most of the nucleon mass via the gluon fields and thus contributes even in the case of vanishing quark masses. We then discuss the contributions to the nucleon mass that do originate from the Higgs mechanism via the quark masses, reviewing the current status of nucleon $\sigma$-terms that encode the corresponding matrix elements.