Eur. Phys. J. C (2011) 71: 1779
https://doi.org/10.1140/epjc/s10052-011-1779-y

Regular Article - Theoretical Physics

Non-linear QCD dynamics in two-photon interactions at high energies

¹ Instituto de Física e Matemática, Universidade Federal de Pelotas, Caixa Postal 354, 96010-900, Pelotas, RS, Brazil
² Centro de Engenharia da Mobilidade, Universidade Federal de Santa Catarina, Campus Universitário, Bairro Bom Retiro, 89219-905, Joinville, SC, Brazil
³ Instituto de Física, Universidade de São Paulo, C.P. 66318, 05315-970, São Paulo, SP, Brazil
⁴ Departamento de Ciências Exatas e da Terra, Universidade Federal de São Paulo, Campus Diadema, Rua Prof. Artur Riedel, 275, Jd. Eldorado, 09972-270, Diadema, SP, Brazil

^* e-mail: barros@ufpel.edu.br

Received: 6 September 2010
Revised: 8 September 2011
Published online: 27 October 2011

Abstract

Perturbative QCD predicts that the growth of the gluon density at high energies should saturate, forming a Color Glass Condensate (CGC), which is described in mean field approximation by the Balitsky–Kovchegov (BK) equation. In this paper we study the γγ interactions at high energies and estimate the main observables which will be probed at future linear colliders using the color dipole picture. We discuss in detail the dipole–dipole cross section and propose a new relation between this quantity and the dipole scattering amplitude. The total γγ, γ ^∗ γ ^∗ cross sections and the real photon structure function are calculated using the recent solution of the BK equation with running coupling constant and the predictions are compared with those obtained using phenomenological models for the dipole–dipole cross section and scattering amplitude. We demonstrate that these models are able to describe the LEP data at high energies, but predict a very different behavior for the observables at higher energies. Therefore we conclude that the study of γγ interactions can be useful to constrain the QCD dynamics.