A Note on Polytopes for Scattering Amplitudes

TL;DR

This paper explores the polytope representation of scattering amplitudes in momentum-twistor space, providing geometric interpretations for tree and loop amplitudes and revealing new triangulation-based representations.

Contribution

It introduces a geometric duality framework for scattering amplitudes using polytopes in extended momentum-twistor spaces, offering new triangulation methods for amplitude representations.

Findings

Polytope volumes correspond to scattering amplitudes.

New triangulations yield simple, cyclic, and local amplitude forms.

Geometric duals provide intrinsic definitions for amplitudes in extended spaces.

Abstract

In this note we continue the exploration of the polytope picture for scattering amplitudes, where amplitudes are associated with the volumes of polytopes in generalized momentum-twistor spaces. After a quick warm-up example illustrating the essential ideas with the elementary geometry of polygons in CP^2, we interpret the 1-loop MHV integrand as the volume of a polytope in CP^3x CP^3, which can be thought of as the space obtained by taking the geometric dual of the Wilson loop in each CP^3 of the product. We then review the polytope picture for the NMHV tree amplitude and give it a more direct and intrinsic definition as the geometric dual of a canonical "square" of the Wilson-Loop polygon, living in a certain extension of momentum-twistor space into CP^4. In both cases, one natural class of triangulations of the polytope produces the BCFW/CSW representations of the amplitudes; another class of triangulations leads to a striking new form, which is both remarkably simple as well as manifestly cyclic and local.