Numerical NLO Calculations for Multiparton Processes - Extending the Subtraction Method to the Virtual Part.

par Christian Reuschle (U. Mainz)

jeudi 16 févr. 2012, 14:30 → 15:30 Europe/Paris

by Christian Reuschle In this talk I report on a recently 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 concentrate on the subtraction terms by showing how the subtraction method is extended to the virtual part, i.e. the one-loop QCD amplitudes. It will be discussed how to derive local subtraction terms for infrared and the ultraviolet regions of the one-loop integration and how these are formulated on the amplitude level rather than on a Feynman diagrammatic level. This allows one to efficiently implement the subtraction terms using recurrence relations, in order to construct one-loop integrands which are locally finite and can be integrated numerically in four dimensions. This method has been successfully applied quite recently to the computation of jet rates in electron-positron annihilation in leading-color approximation and I will present the results for up to seven jets, which are new.