English Intern
  • Seminar Elementarteilchenphysik
Theoretische Physik II

Dr. Valentin Hirschi


T a l k : 21. October 2021

Local Unitarity: let infrared divergences cancel by themselves


The canonical approach for tackling higher-order computations involves splitting up a finite quantity into two separately divergent ones. First, multiloop amplitudes are evaluated using (mostly) analytical techniques. Second, phase-space integrals are computed using numerical Monte-Carlo techniques with ad-hoc subtraction terms for regularising soft and/or collinear infrared divergences.

I will present our work of developing a radically new paradigm, Local Unitarity, in which infrared singularities in real-emission and virtual degrees of freedom directly cancel without the use of any counterterms and at any perturbative order. The deeper connections between Local Unitarity and the KLN theorem naturally lead to a novel treatment of initial state singularities, which differs from the traditional collinear mass factorization and connects more directly to the physics of hadron collisions.

On the practical side, Local Unitarity allows for the fully numerical computation of differential corrections, potentially alleviating the complexity bottleneck analytical alternatives are facing. From a theoretical standpoint, our proof of the local cancellation of infrared singularities sheds new light on the exact mechanism by which it is realized in Quantum Field Theories.