Generalized Parton Distributions and Their Singularities

Understand

A new approach to building models of generalized parton distributions (GPDs) is discussed that is based on the factorized DD (double distribution) Ansatz within the single-DD formalism.

• The latter was not used before, because reconstructing GPDs from the forward limit one should start in this case with a very singular function f({\beta})/{\beta} rather than with the usual parton density f({\beta}).
• This results in a non-integrable singularity at {\beta}=0 exaggerated by the fact that f({\beta})'s, on their own, have a singular {\beta}^{-a} Regge behavior for small {\beta}.
• It is shown that the singularity is regulated within the GPD model of Szczepaniak et al., in which the Regge behavior is implanted through a subtracted dispersion relation for the hadron-parton scattering amplitude.