Scattering AMplitudes from Unitarity-based Reduction Algorithm at the Integrand-level

TL;DR

SAMURAI is an automated tool that efficiently computes one-loop scattering amplitudes using unitarity-based reduction at the integrand level, aiding next-to-leading order calculations for collider physics.

Contribution

It extends the OPP-approach with generalized d-dimensional unitarity cuts and polynomial interpolation, providing a versatile, publicly available library for amplitude evaluation.

Findings

Successfully applied to photon and quark scattering processes

Demonstrates efficiency and automation in NLO calculations

Supports integrand decomposition and numerical evaluation

Abstract

SAMURAI is a tool for the automated numerical evaluation of one-loop corrections to any scattering amplitudes within the dimensional-regularization scheme. It is based on the decomposition of the integrand according to the OPP-approach, extended to accommodate an implementation of the generalized d-dimensional unitarity-cuts technique, and uses a polynomial interpolation exploiting the Discrete Fourier Transform. SAMURAI can process integrands written either as numerator of Feynman diagrams or as product of tree-level amplitudes. We discuss some applications, among which the 6- and 8-photon scattering in QED, and the 6-quark scattering in QCD. SAMURAI has been implemented as a Fortran90 library, publicly available, and it could be a useful module for the systematic evaluation of the virtual corrections oriented towards automating next-to-leading order calculations relevant for the LHC phenomenology.