A Demonstration of Hadron Mass Origin from QCD Trace Anomaly

TL;DR

This paper presents the first lattice QCD calculation demonstrating that the gluon trace anomaly is the primary contributor to the nucleon mass, supporting the QCD origin of hadron masses beyond the Higgs mechanism.

Contribution

It provides the first direct lattice QCD evidence quantifying the gluon trace anomaly contribution to hadron masses, confirming theoretical predictions.

Findings

Gluon trace anomaly accounts for most of the nucleon mass.

Pion's gluon trace anomaly contribution is significantly smaller.

Gluon trace anomaly coefficient matches theoretical expectations.

Abstract

Quantum chromodynamics (QCD) claims that the major source of the nucleon invariant mass is not the Higgs mechanism but the trace anomaly in QCD energy momentum tensor. Although experimental and theoretical results support such conclusion, a direct demonstration is still absent. We present the first Lattice QCD calculation of the quark and gluon trace anomaly contributions to the hadron masses, using the overlap fermion on the 2+1 flavor dynamical Domain wall quark ensemble at $m_{\pi}=340$ MeV and lattice spacing $a=$0.1105 fm. The result shows that the gluon trace anomaly contributes to most of the nucleon mass, and the contribution in the pion state is smaller than that in others nearly by a factor $\sim$10 since the gluon trace anomaly density inside pion is different from the other hadrons and the magnitude is much smaller. The gluon trace anomaly coefficient $\beta/g^3=-0.056(6)$ we obtained is consistent with its regularization independent leading order value $(-11+\frac{2N_f}{3})/(4\pi)^2$ perfectly.