Samurai

Synopsis

Samurai is the abbreviation for Scattering AMplitudes from Unitarity-based Reduction Algorithm at the Integrand level.

Overview

Samurai is a tool for the automated numerical evaluation of one-loop virtual 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 generalised D-dimensional unitarity-cuts technique, and uses a polynomial interpolation exploiting the Discrete Fourier Transform. Samurai can process integrands with any number of external legs, written either as numerator of Feynman diagrams or as product of tree level amplitudes and it can be compiled in double or quadruple precision.

Authors

• P. Mastrolia, <pierpaolo.mastrolia[AT]cern.ch>
• G. Ossola, <gossola[AT]citytech.cuny.edu>
• T. Reiter, <reiterth[AT]mpp.mpg.de>
• F. Tramontano, <francesco.tramontano[AT]cern.ch>

Publications

1. P. Mastrolia, G. Ossola, T. Reiter, F. Tramontano, "Scattering AMplitudes from Unitarity-based Reduction Algorithm at the Integrand-level, " JHEP 1008 (2010) 080, arXiv:1006.0710 [hep-ph]

Download

The source is available as a tar'ed and gzip'ed package, which extracts the files into a directory called samurai_v1.0. The compilation can be done by running the Install command. This will also compile the two packages for the evaluation of the scalar integrals: QCDLOOP and AVH-OLO. The code has been developed and tested under Ubuntu and Mac OSX, please report any compilation problems under other operating systems to the authors.

• samurai-2.1.1.tar.gz
• samurai-2.0.0.tar.gz
• samurai_v1.0.tar.gz
• manual (PDF)

Examples

The distribution contains a dedicated directory with examples of calculations performed with Samurai. The examples could be used as a guide to understand the framework, as templates to generate the codes for other virtual processes or to design an interface with other tools.

1. Examples with integrands given as numerators of Feynman diagrams
   • 6-point rank-6 numertator function
   • 4-photon scattering amplitudes
   • 6-photon scattering amplitudes
   • 8-photon scattering amplitudes
   • Triangle diagram relevant for Drell-Yan process
   • Leading color amplitudes for VB+jet production
   • 6-quark scattering amplitudes
     • For this example the generation of the integrands has been fully automatized with a private infrastructure derived from golem-2.0
2. Examples with integrands given as product of tree level amplitudes
   • Scalar contribution to 5-gluon all-plus helicity amplitude
   • Scalar contribution to 6-gluon all-plus helicity amplitude

Related Codes

A package for the evaluation of the scalar integrals needs to be linked to Samurai to get full numerical results. Samurai has been linked to the following two libraries:

• QCDLOOP
• AVH-OLO