Towards the Gravituhedron: new expressions for NMHV gravity amplitudes
Jaroslav Trnka
Abstract
A bstract 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 $$ \mathcal{G} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>G</mml:mi> </mml:math> -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 $$ \mathcal{G} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>G</mml:mi> </mml:math> -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.