The real corrections to the virtual photon impact factor

We investigate the interaction of two virtual photons in the high energy limit of quantum chromodynamics (QCD). We are motivated by two closely linked problems: the calculation of the #gamma#"*#gamma#"* total cross section, #sigma#"#gamma#""*"#gamma#""*, in the framework NLO BFKL and the NLO extensions to the colour dipole picture. We calculate the squared amplitude for the process #gamma#"* + q #-># qqg + q in arbitrary space-time dimensions for both longitudinal and transverse photon polarisation. In transverse configuration space the result is found to factorise supporting in this way the photon wave function interpretation. This is the first step in the calculation of the qqg Fock component of the #gamma#"* wave function. The squared vertex for the transition Reggeon-#gamma#"* #-># qqg is extracted in order to calculate the NLO real corrections to the #gamma#"* impact factor. Together with the virtual corrections this will allow for the calculation of #sigma#"#gamma#""*"#gamma#""*. The infrared divergences are dimensionally regularised and their cancellation against those from the virtual corrections is performed. After the introduction of Feynman parameters in each Feynman diagram, part of the qqg phase space integration is performed analytically. The various divergences emerging due to the independent treatment of the diagrams are regularised. A procedure is worked out to obtain for each diagram a finite phase space integral. In the case of longitudinal photon polarisation, this method is implemented in a computer program and the full phase space integration is carried out numerically. First numerical tests of the calculation are successfully performed. (orig.)SIGLEAvailable from TIB Hannover: RA 8919(2003-036) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman