Towards the Gravituhedron: New Expressions for NMHV Gravity Amplitudes

TL;DR

This paper introduces new explicit formulas and a graphical framework for n-point NMHV gravity amplitudes, proposing a potential geometric interpretation via a Gravituhedron, inspired by Yang-Mills theory.

Contribution

It defines G-invariants as gravity analogues of R-invariants and provides explicit NMHV gravity amplitude formulas up to eight points, suggesting a new geometric structure.

Findings

Explicit formulas for NMHV gravity amplitudes up to eight points

Introduction of G-invariants as gravity analogues of R-invariants

Discussion of connections to BCFW, momentum twistors, and potential Gravituhedron geometry

Abstract

In this paper, we present new expressions for n-point NMHV tree-level gravity amplitudes. We introduce a method of factorization diagrams which is a simple graphical representation of R-invariants in Yang-Mills theory. We define the gravity analogues which we call G-invariants, and expand the NMHV gravity amplitudes in terms of these objects. We provide explicit formulas of NMHV gravity amplitudes up to eight points in terms of G-invariants, and give the general definition for any number of points. We discuss the connection to BCFW representation, special behavior under large momentum shift, the role of momentum twistors and the intricate web of spurious poles cancelation. Because of the close connection between R-invariants and the (tree-level) Amplituhedron for Yang-Mills amplitudes, we speculate that the new expansion for gravity amplitudes should correspond to the triangulation of the putative Gravituhedron geometry.