Eur. Phys. J. C (2015) 75: 184
https://doi.org/10.1140/epjc/s10052-015-3387-8

Regular Article - Theoretical Physics

New contributions to gluon poles in direct photon production

Bogoliubov Laboratory of Theoretical Physics, JINR, 141980, Dubna, Russia

^* e-mail: anikin@theor.jinr.ru

Received: 24 January 2015
Accepted: 31 March 2015
Published online: 1 May 2015

Abstract

We consider the direct photon production in a two hadron collision with one of the hadrons transversely polarized. By using the contour gauge for gluon fields, we find that there are new twist- terms present in the hadron tensor of the considered process in addition to the standard twist- terms. In this work, we demonstrate that the significance of these new terms are twofold: first, they are crucial to both the QED and the QCD gauge invariance and, second, their contributions to the hadron tensor are at least the same as those from the standard ones. We also study the resulting effects which are responsible for the universality breaking of the corresponding twist- parton distributions.