Gravitational form factors of the baryon octet in holographic QCD

TL;DR

This work addresses the gravitational structure of the baryon octet by computing the gravitational form factor $A(Q^2)$ within a bottom-up holographic QCD model that incorporates SU(3) flavor breaking through the strange quark mass. Using two bulk spinors for each baryon and a chiral-symmetry-breaking scalar $X$, the model fixes seven parameters from octet mass spectra and then predicts $A(Q^2)$ and the gravitational radii across the octet via overlap with the bulk graviton mode. The results show a consistent fall-off of $A(Q^2)$ with $Q^2$, with hyperons exhibiting smaller gravitational radii due to strangeness, and good agreement with lattice QCD in the non-strange sector. These findings extend holographic studies of GFFs from the nucleon to the full baryon octet, highlighting how explicit and dynamical chiral symmetry breaking shapes the spatial energy-momentum distributions in hadrons and suggesting avenues for exploring the $D$-term and gluonic EMT components in future work.

Abstract

The gravitational form factors (GFFs) of the baryon octet, including hyperons, are investigated in a bottom-up holographic QCD model that explicitly incorporates the SU(3) flavor symmetry breaking through the strange quark mass. We fit the model parameters to reproduce the empirical masses of the baryon octet and examine the dependence of GFFs on the probe momentum. Our numerical results show distinct differences in the GFFs across the baryon octet. The computed GFFs are found to be in reasonable agreement with available lattice QCD results for the non-strange/nucleon sector. We also calculate the gravitational radii of the baryon octet and find that they decrease with increasing strangeness, indicating that heavier hyperons are more compact.

Figures (1)

• Figure 1: The GFF $A(Q^2)$ of the baryon octet as a function of $Q^2$. Data points with error bars represent lattice QCD results Hackett:2023rif for the proton. The model curves are shown as red solid for $p$, dashed for $\Lambda$, dotted for $\Sigma$, and dash‐dotted for $\Xi$. The black double dash-dotted line denotes the prediction for the proton in the chiral limit obtained with a holographic QCD model Abidin:2008hn.