Soft theorem to three loops in QCD and $$ \mathcal{N} $$ = 4 super Yang-Mills theory
Wen Chen, M. X. Luo, Tong-Zhi Yang, Hua Xing Zhu
Abstract
A bstract The soft theorem states that scattering amplitude in gauge theory with a soft gauge-boson emission can be factorized into a hard scattering amplitude and a soft factor. In this paper, we present calculations of the soft factor for processes involving two hard colored partons, up to three loops in QCD. To accomplish this, we developed a systematic method for recursively calculating relevant Feynman integrals using the Feynman-Parameter representation. Our results constitute an important ingredient for the subtraction of infrared singularities at N 4 LO in perturbative QCD. Using the principle of leading transcendentality between QCD and $$ \mathcal{N} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>N</mml:mi> </mml:math> = 4 super Yang-Mills theory, we determine the soft factor in the latter case to three loops with full-color dependence. As a by-product, we also obtain the finite constant $$ {f}_2^{(3)} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msubsup> <mml:mi>f</mml:mi> <mml:mn>2</mml:mn> <mml:mfenced> <mml:mn>3</mml:mn> </mml:mfenced> </mml:msubsup> </mml:math> in the Bern-Dixon-Smirnov ansatz analytically, which was previously known numerically only.