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T: Fachverband Teilchenphysik

T 12: QCD (Theorie) / Quantenfeldtheorie

T 12.6: Vortrag

Freitag, 1. April 2011, 15:20–15:35, 30.23: 10-1

Numerical NLO QCD calculations - Contour deformation — •Sebastian Becker — Institut für Physik, Universität Mainz, D - 55099 Mainz,Germany

This talk reports on a previously published algorithm for the numerical calculation of one-loop QCD amplitudes. The algorithm consists of subtraction terms, approximating the soft, collinear and ultraviolet divergences of one-loop amplitudes and a method to deform the integration contour for the loop integration into the complex space. It is formulated at the amplitude level and does not rely on Feynman graphs. Therefore all required ingredients can be calculated efficiently using recurrence relations.

The Talk will present the algorithm for the contour deformation for the loop integration. Our starting point is an integrand of a finite one-loop QCD amplitude, i.e. a one-loop QCD amplitude where all the infrared and ultraviolet divergences are subtracted. It will discuss that such an integrand is still not numerical integrable in the real space and that we have to deform our integration region into the complex plane. The algorithm is based on the introduction of Feynman parameters, the deformation of the loop momentum and the Feynman parameters in the complex plane and the expansion of the true propagators around propagators where we have added a small mass µ_IR.