Polynomial reduction and evaluation of tree- and loop-level CHY amplitudes

TL;DR

This paper introduces a polynomial reduction method transforming CHY amplitude integrands into a standard form with a specific monomial structure, enabling simplified evaluation of tree and one-loop amplitudes via residues at infinity.

Contribution

It presents a novel polynomial reduction procedure and a residue-based evaluation method for CHY amplitudes, applicable at tree and one-loop levels.

Findings

Standard form polynomials have finite size at any n

A complete basis of monomials spans the polynomial space

Explicit residue evaluation simplifies amplitude calculations

Abstract

We develop a polynomial reduction procedure that transforms any gauge fixed CHY amplitude integrand for $n$ scattering particles into a $\sigma$-moduli multivariate polynomial of what we call the $\textit{standard form}$. We show that a standard form polynomial must have a specific $\textit{ladder type}$ monomial structure, which has finite size at any $n$, with highest multivariate degree given by $(n-3)(n-4)/2$. This set of monomials spans a complete basis for polynomials with rational coefficients in kinematic data on the support of scattering equations. Subsequently, at tree and one-loop level, we employ the global residue theorem to derive a prescription that evaluates any CHY amplitude by means of collecting simple residues at infinity only. The prescription is then applied explicitly to some tree and one-loop amplitude examples.