The electromagnetic form factors of nucleons are calculated using an AdS/QCD
model by considering a Dirac field coupled to a vector field in the
5-dimensional AdS space. We also calculate a gravitational or energy-momentum
form factor by perturbing the metric from the static AdS solution. We consider
both the hard-wall model where the AdS geometry is cutoff at z_0 and the
soft-wall model where the geometry is smoothly cut off by a background dilaton
field.Comment: 9 pages, 3 figures, version 2 has added references and version 3
fixes some typo
We consider in detail the mass operator analysis for the nonstrange lϭ1 excited baryons in large N c QCD. We present a straightforward procedure for constructing the large N c baryon wave functions, and provide complete analytic expressions for the matrix elements of all the independent isosinglet mass operators. We discuss the relationship between the old-fashioned operator analyses based on nonrelativistic SU͑6͒ symmetry and the modern large N c approach, which has a firmer theoretical foundation. We then suggest a possible dynamical interpretation for the subset of operators preferred strongly by the data. ͓S0556-2821͑99͒07809-1͔
We estimate the two-photon exchange contribution to elastic electron-proton scattering at large momentum transfer through the scattering off a parton in the proton. We relate the two-photon exchange amplitude to the generalized parton distributions which appear in hard exclusive processes. We find that when taking the polarization transfer determinations of the form factors as input, adding in the 2-photon correction does reproduce the Rosenbluth cross sections.
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