Positive geometry, local triangulations, and the dual of the Amplituhedron

TL;DR

This paper explores local positive geometries related to the Amplituhedron in scattering amplitudes, revealing sign-flip conditions, new geometries, and their relation to dual spaces, advancing understanding of amplitude structures in supersymmetric theories.

Contribution

It introduces the concept of local positive spaces characterized by sign-flip conditions, constructs new geometries from these spaces, and identifies their relation to the dual Amplituhedron, expanding geometric understanding of scattering amplitudes.

Findings

Local positive spaces are characterized by sign-flip conditions.

Maximal sign-flip spaces are finite one-loop octagons.

Pentagons do not triangulate the Amplituhedron but its twin 'Amplituhedron-Prime'.

Abstract

We initiate the systematic study of \emph{local positive spaces} which arise in the context of the Amplituhedron construction for scattering amplitudes in planar maximally supersymmetric Yang-Mills theory. We show that all local positive spaces relevant for one-loop MHV amplitudes are characterized by certain sign-flip conditions and are associated with surprisingly simple logarithmic forms. In the maximal sign-flip case they are finite one-loop octagons. Particular combinations of sign-flip spaces can be glued into new local positive geometries. These correspond to local pentagon integrands that appear in the local expansion of the MHV one-loop amplitude. We show that, geometrically, these pentagons do \emph{not} triangulate the original Amplituhedron space but rather its twin "Amplituhedron-Prime." This new geometry has the same boundary structure as the Amplituhedron (and therefore the same logarithmic form) but differs in the bulk as a geometric space. On certain two-dimensional boundaries, where the Amplituhedron geometry reduces to a polygon, we check that both spaces map to the same dual polygon. Interestingly, we find that the pentagons internally triangulate that dual space. This gives a direct evidence that the chiral pentagons are natural building blocks for a yet-to-be discovered dual Amplituhedron.