We introduce a prescriptive approach to generalized unitarity, resulting in a strictly-diagonal basis of loop integrands with coefficients given by specifically-tailored residues in field theory. We illustrate the power of this strategy in the case of planar, maximally supersymmetric Yang-Mills theory, where we construct closed-form representations of all (n-point NkMHV) scattering amplitudes through three loops. The prescriptive approach contrasts with the ordinary description of unitarity-based methods by avoiding any need for linear algebra to determine integrand coefficients. We describe this approach in general terms as it should have applications to many quantum field theories, including those without planarity, supersymmetry, or massless spectra defined in any number of dimensions.
@article{arxiv.1704.05460,
title = {Prescriptive Unitarity},
author = {Jacob L. Bourjaily and Enrico Herrmann and Jaroslav Trnka},
journal= {arXiv preprint arXiv:1704.05460},
year = {2017}
}