New Parametrization for Generalized Parton Distributions with Non-Zero Skewedness

We present a physically motivated parameterization for the unpolarized generalized parton distributions of the nucleon, $H(X,\zeta,t$) and $E(X,\zeta,t)$, obtained from Deeply Virtual Compton Scattering (DVCS) experiments, where $X$ is the struck parton's momentum fraction, $\zeta$, skewedness parameter, is the fraction of longitudinal momentum transfer between the incoming (virtual) photon and the outgoing photon, and $t$ is the four-momentum transfer squared. At variance with other physically constrained parametrizations available in the literature [1,2], ours is the first one that applies to both zero and non-zero values of the skewedness parameter, $\zeta$. We define $H$ and $E$ using overlap integrals of the nucleon light-cone wave functions at large values of $X$ [3], and assuming Regge behavior at low $X$. At $\zeta$ = 0 we use the constraints provided by simultaneous fits to experimental data on both the elastic nucleon form factors and the ``forward'' parton distributions from deep inelastic scattering. Our results at $\zeta$ = 0 are of the same quality of the ones obtained in [1,2]. In order to extend our parametrization to $\zeta \neq$ 0, we work out additional constraints from recent lattice calculations of higher moments of generalized parton distributions [4]. [1] M. Diehl, T. Feldmann, R. Jakob and P. Kroll, Eur. Phys. J. C \textbf{39}, 1 (2005) [2] M. Guidal, M. V. Polyakov, A. V. Radyushkin and M. Vanderhaeghen, Phys. Rev. D \textbf{72}, 054013 (2005) [3] S. J. Brodsky, M. Diehl and D. S. Hwang, Nucl. Phys. B \textbf{596}, 99 (2001) [4] G. Schierholz and J. Zanotti, \textit{private communication}.