Generalized baryon form factors and proton structure functions in the   Sakai-Sugimoto model
  We investigate the production of positive parity baryon resonances in proton electromagnetic scattering within the Sakai-Sugimoto model. The latter is a string model for the non-perturbative regime of large $N_c$ QCD. Using holographic techniques we calculate the generalized Dirac and Pauli form factors that describe resonance production. We use these results to estimate the contribution of resonance production to the proton structure functions. Interestingly, we find an approximate Callan-Gross relation for the structure functions in a regime of intermediate values of the Bjorken variable. 
C. A. Ballon Bayona, Henrique Boschi-Filho, Nelson R. F. Braga,   Matthias Ihl, Marcus A. C. Torres
hep-ph hep-th