Maximal Unitarity at Two Loops

TL;DR

This paper presents a method to compute double box integral coefficients in massless four-point amplitudes using maximal unitarity, contour choices, and consistency equations, applicable analytically or numerically.

Contribution

It introduces a novel approach for calculating two-loop amplitude coefficients via maximal unitarity and contour integration, with a focus on consistency conditions.

Findings

Derived explicit formulas for double box coefficients

Established contour selection criteria for unitarity cuts

Demonstrated applicability to analytical and numerical computations

Abstract

We show how to compute the coefficients of the double box basis integrals in a massless four-point amplitude in terms of tree amplitudes. We show how to choose suitable multidimensional contours for performing the required cuts, and derive consistency equations from the requirement that integrals of total derivatives vanish. Our formulae for the coefficients can be used either analytically or numerically.