Poles At Infinity in On-shell Diagrams

TL;DR

This paper investigates poles at infinity in on-shell diagrams within non-maximally supersymmetric Yang-Mills theories, revealing their origin from loop pinching and non-planar twists, and linking them to non-planar on-shell functions.

Contribution

It introduces a diagrammatic interpretation of UV poles at infinity as loop pinching and non-planar twists, extending the understanding of on-shell diagrams beyond maximally supersymmetric cases.

Findings

UV poles at infinity originate from loop pinching and non-planar twists.

These poles do not correspond to edge removal, unlike IR poles.

The work connects poles at infinity to non-planar on-shell functions.

Abstract

In this paper we study on-shell diagrams in ${\cal N}{<}4$ supersymmetric Yang-Mills (SYM) theory. These are on-shell gauge invariant objects which appear as cuts of loop integrands in the context of generalized unitarity and serve as building blocks for amplitudes in recursion relations. In the dual formulation, they are associated with cells of the positive Grassmannian $G_+(k,n)$ and the on-shell functions can be reproduced as canonical differential forms. While for the case of the ${\cal N}{=}4$ maximally supersymmetric Yang-Mills theory all poles in on-shell diagrams correspond to IR poles when the momentum flows in edges are zero, for ${\cal N}{<}4$ SYM theories there are new UV poles when the loop momenta go to infinity. These poles originate from the prefactor of the canonical dlog form and do not correspond to erasing edges in on-shell diagrams. We show that they can be interpreted as a diagrammatic operation which involves pinching a loop and performing a ``non-planar twist'' on external legs, which gives rise to a non-planar on-shell diagram. Our result provides an important clue on the role of poles at infinite momenta in on-shell scattering amplitudes, and the relation to non-planar on-shell functions.