Generalized Permutohedra, Scattering Amplitudes, and a Cubic Three-Fold

Abstract

In this note, we apply combinatorial techniques from our Ph.D. thesis to study how generalized permutohedra may be represented functionally on Parke-Tayor factors and related rational functions. In any functional representation of polyhedral cones, in general certain homological information may be lost. The combinatorial relations of the Parke-Taylor factors lift homologically to generalized permutohedra. The 6-particle case contains several related layers of interesting geometric data: the Newton polytope for the polynomial numerator lifts the permutohedron in three variables, which is a hexagon, and the fraction itself provides a functional representation of certain neighborhoods of a vertex of a 5-dimensional weight permutohedron. The lift from fraction to generalized permutohedron was derived by comparing functional representations. We observe additionally that the numerator and its permutations satisfy a degree 3 polynomial relation which defines a classical projective variety known as the Segre cubic. We include in an extended Appendix selected Mathematica code which can be used to verify our computations independently.