Gravitational form factors of the baryon octet and flavor dependence in an NJL quark--diquark model

Abstract

We calculate the gravitational form factors of the baryon octet in a proper-time-regulated Nambu--Jona-Lasinio quark--diquark model using the total energy--momentum tensor. The momentum, angular-momentum and stress form factors reveal different flavor dependences, and the momentum and stress slope radii follow distinct hierarchies. With the diquark pole inputs taken from the hadron-spectrum calculation, the $Σ$ is more compact than the nucleon in its momentum response but more extended in its normalized stress response; it also has the smallest magnitude of the forward stress form factor. This combination of weaker forward strength and larger normalized extent persists under separate variations of the scalar and axial-vector diquark couplings. Along a self-consistent flavor-breaking path the initially degenerate radii split, and the sampled $Σ$--nucleon stress-radius ordering changes while the momentum ordering does not. The metric continuation and external pole inputs further change these hierarchies. Together, the octet form factors show how flavor breaking and scalar and axial-vector correlations affect momentum and stress differently.