The European Physical Journal A (EPJ A)

Issue		Eur. Phys. J. A Volume 40, Number 2, May 2009
Page(s)		181 - 198
Section		Regular Article - Theoretical Physics
DOI		10.1140/epja/i2008-10759-2
Published online		18 April 2009

Eur. Phys. J. A 40, 181-198 (2009)
DOI: 10.1140/epja/i2008-10759-2

Dual parametrization of GPDs versus the double distribution Ansatz

M. V. Polyakov^{1, 2} and K. M. Semenov-Tian-Shansky^{1, 3}

¹ Institut für Theoretische Physik II, Ruhr-Universität Bochum, D-44780, Bochum, Germany
² Petersburg Nuclear Physics Institute, 188350, Gatchina, St. Petersburg, Russia
³ St. Petersburg State University, 198504, St. Petersburg, Petrodvoretz, Russia

Maxim.Polyakov@tp2.ruhr-uni-bochum.de
semenovk@tp2.ruhr-uni-bochum.de

Received 26 November 2008 / Revised version 4 March 2009 / Published online 18 April 2009

Abstract

We establish a link between the dual parametrization of GPDs and a popular parametrization based on the double distribution Ansatz, which is in prevalent use in phenomenological applications. We compute several first forward-like functions that express the double distribution Ansatz for GPDs in the framework of the dual parametrization and show that these forward-like functions make the dominant contribution into the GPD quintessence function. We also argue that the forward-like functions $\ensuremath Q_{2 \nu} (x)$ with $\nu$ $\ge$ 1 contribute to the leading singular small-x_Bj behavior of the imaginary part of DVCS amplitude. This makes the small-x_Bj behavior of ${\rm Im}\ensuremath A^$ independent of the asymptotic behavior of PDFs. Assuming analyticity of Mellin moments of GPDs in the Mellin space we are able to fix the value of the D -form factor in terms of the GPD quintessence function N(x, t) and the forward-like function Q ₀(x, t) .

PACS
13.60.Fz - Elastic and Compton scattering.
11.55.Hx - Sum rules.

Correspondence: semenovk@tp2.ruhr-uni-bochum.de

Communicated by A. Schäfer

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