Constructing multi-loop scattering amplitudes with manifest singularity structure

Abstract

The infrared exponentiation properties of dimensionally-regularized multi-loop scattering amplitudes are typically hidden at the level of the integrand, materializing only after integral evaluation. We address this long-standing problem by introducing an appropriate integral basis which is simultaneously finite and uniform weight. As an example, we cast the integrand for the QCD corrections to the two-loop massless quark electromagnetic form factor into a form where it is manifest that the ${\epsilon }^{-4}$ and ${\epsilon }^{-3}$ pole terms arise from the $\epsilon$ expansion of the square of our one-loop master integral.

8 pages; in v2: references added relative to v1; in v3: introduction expanded and examples added along the lines suggested by the referees, further references and note added