Investigating generalized parton distribution in gravity dual

Generalized parton distribution (GPD) contains rich information of partons in a hadron, including transverse profile, and is also non-perturbative information necessary in describing a variety of hard processes, such as meson leptoproduction and double deeply virtual Compton scattering (DDVCS). In order to unveil non-perturbative aspects of GPD, we study DDVCS at small x in gravitational dual description. Using the complex spin j-plane representation of DDVCS amplitude, we show that GPD is well-defined and can be extracted from the amplitude even in the strong coupling regime. It also turns out that the saddle point value in the j-plane representation plays an important role; there are two phases in the imaginary part of amplitude of DDVCS and GPD, depending on relative position of the saddle point and the leading pole in the j-plane, and crossover between them is induced by the change of the kinematical variables. The saddle point value also directly controls kinematical variable dependence of many observables in one of the two phases, and indeed the dependence is qualitatively in nice agreement with HERA measurements. This Letter also serves as a brief summary of a preprint arxiv:arXiv:1105.2999.