Mechanical structure of the nucleon and the baryon octet: Twist-2 case

TL;DR

This paper analyzes the flavor decomposition of gravitational form factors of the nucleon and baryon octet using a pion mean-field approach, highlighting the roles of twist-2 and twist-4 operators in QCD.

Contribution

It provides a detailed flavor decomposition of GFFs within a large N_c QCD framework, emphasizing the importance of twist-4 operators often neglected in similar studies.

Findings

Strange quark effects are mild for mass and angular momentum GFFs.

Strange quark contributions significantly affect the D-term form factor.

Twist-4 operators are crucial and of order unity, unlike suppressed twist-2 gluonic contributions.

Abstract

We investigate the gravitational form factors (GFFs) of the nucleon and the baryon octet, decomposed into their flavor components, utilizing a pion mean-field approach grounded in the large $N_c$ limit of Quantum Chromodynamics (QCD). Our focus is on the contributions from the twist-2 operators to the flavor-triplet and octet GFFs, and we decompose the mass, angular momentum, and $D$-term form factors of the nucleon into their respective flavors. The strange quark contributions are found to be relatively mild for the mass and angular momentum form factors, while providing significant corrections to the $D$-term form factor. In the course of examining the flavor decomposition of the GFFs, we uncover that the effects of twist-4 operators play a crucial role. While the gluonic contributions are suppressed by the packing fraction of the instanton vacuum in the twist-2 case, contributions from twist-4 operators are of order unity, necessitating its explicit consideration.