Gravitational form factors and mechanical properties of the nucleon in a meson dominance approach

Abstract

We analyze the gravitational form factors and mechanical properties of the nucleon, focusing on both some general issues as well as on modeling with meson dominance. We show that the lattice QCD results for the nucleon gravitational form factors at $m_\pi=170$~MeV, available for space-like momentum transfer squared up to 2GeV, are explained in a natural way within the meson dominance approach. We carry out the proper Raman spin decomposition of the energy-momentum tensor and in each spin channel use a minimum number of resonances consistent with the perturbative QCD short-distance constraints. These constraints are related to the super-convergence sum rules, following from the asymptotic perturbative QCD fall-off of the form factors. The value of the nucleon $D$-term following from the fits is -3.0(4). Next, we obtain the two-dimensional transverse gravitational densities of the nucleon in the transverse coordinate $b$. With the super-convergence sum rules, we derive new sum rules for these densities at the origin and for their derivatives, involving logarithmic weighting in the corresponding spectral density integrals. From analysis of the threshold behavior in the time-like region and the properties of the $\pi\pi \to N\bar{N}$ reaction, we infer the behavior of the transverse densities at asymptotically large coordinates. We also carry out the meson dominance analysis of the two- and three-dimensional mechanical properties of the nucleon (the pressure and stress) and explore their connection to the spectral densities via dispersion relations.