Nucleon mass radii and distribution: Holographic QCD, Lattice QCD and GlueX data

We briefly review and expand our recent analysis for all three invariant A, B, D gravitational form factors of the nucleon in holographic QCD. They compare well to the gluonic gravitational form factors recently measured using lattice QCD simulations. The holographic A-term is fixed by the tensor T=2++ (graviton) Regge trajectory, and the D-term by the difference between the tensor T=2++ (graviton) and scalar S=0++ (dilaton) Regge trajectories. The B-term is null in the absence of a tensor coupling to a Dirac fermion in bulk. A first measurement of the tensor form factor A-term is already accessible using the current GlueX data, and therefore the tensor gluonic mass radius, pressure, and shear inside the proton, thanks to holography. The holographic A-term and D-term can be expressed exactly in terms of harmonic numbers. The tensor mass radius from the holographic threshold is found to be ⟨rGT2⟩≈(0.57–0.60 fm)2, in agreement with ⟨rGT2⟩≈(0.62 fm)2 as extracted from the overall numerical lattice data, and empirical GlueX data. The scalar mass radius is found to be slightly larger ⟨rGS2⟩≈(0.7 fm)2.

Note:

16 pages, 4 figures

Strong Interactions
form factor: gravitation
form factor: tensor
quantum chromodynamics: holography
coupling: tensor
nucleon: mass
mass: scalar
nucleon: form factor
fermion: Dirac
lattice field theory

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