Gravitational form factors of baryons in a spectator diquark model

TL;DR

The paper tackles how the energy–momentum tensor $T^{\tau \mu \nu}$, and its gravitational form factors, encode the transverse spin structure of baryons and relate to chiral-odd GPDs $H_T$, $E_T$, $\tilde{H}_T$, and $\tilde{E}_T$ via Mellin moments. It adopts a diquark spectator model within the light-cone framework to compute the GFFs for the proton and the light hyperon $\Xi^0$, modeling the baryon as an active quark plus a scalar or axial-vector diquark with dipolar baryon–quark–diquark vertices. The tensor-current GFFs, including $A_{T20}(t)$, $\bar{A}_{T20}(t)$, $B_{T20}(t)$, and $\bar{B}_{T21}(t)$, are connected to the chiral-odd GPDs through Mellin moments, with zero skewness simplifying to transverse momentum transfer and enabling evaluation via LCWF overlaps. Numerically, the authors observe clear flavor dependence: $A_{T20}(0)$ and $\bar{B}_{T20}(0)$ for $u$ quarks differ between the proton and $\Xi^0$, exhibiting complementary behavior and aligning qualitatively with BLFQ benchmarks, thereby validating the diquark framework as a practical tool for probing gravitational form factors and their GPD connections.

Abstract

Energy momentum tensor (EMT) expresses the interaction between the gravitation and the matter fields, in which the scattering off the graviton is a natural but infeasible probe. However, the EMT can be accessed indirectly through electromagnetic interactions in quantum chromodynamics. The matrix elements of the local EMT operator are parameterized by gravitational form factors, which are subsequently related to the generalized parton distributions. Within the diquark spectator model, we investigate the gravitational form factors of baryons. We consider all the feasible pairs of quark-diquark systems to understand the behavior of each constituent quark flavor of strange and non-strange baryons.

Figures (1)

• Figure 1: Comparison of gravitational form factors (a) $A_{T20}(t)$ and (b) $\bar{B}_{T20}(t)$ as a function of transverse momentum transfer $t$ (GeV$^2$) for $u$ quark flavor of proton and $\Xi^0$.