CAMORRA: A C++ library for recursive computation of particle scattering amplitudes

We present a new Monte Carlo tool that computes full tree-level matrix elements in high-energy physics. The program accepts user-defined models and has no restrictions on the process multiplicity. To achieve acceptable performance, CAMORRA evaluates the matrix elements in a recursive way by combining off-shell currents. Furthermore, CAMORRA can be used to compute amplitudes involving continuous color and helicity final states.Program summaryProgram title: CAMORRACatalogue identifier: AEHN_v1_0Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEHN_v1_0.htmlProgram obtainable from: CPC Program Library, Queen's University, Belfast, N. IrelandLicensing provisions: GPL version 2No. of lines in distributed program, including test data, etc.: 252 572No. of bytes in distributed program, including test data, etc.: 1 711 469Distribution format: tar.gzProgramming language: C++Computer: AllOperating system: Tested on Linux and Mac OS, but should work on any systemClassification: 4.4Nature of problem: Current recursive matrix element computation programs are confined to standard model amplitudes, whereas many new physics signatures and backgrounds at hadron colliders are associated with multi-parton final states.Solution method: The library applies the Berends–Giele/Caravaglios–Moretti recursive algorithm in a generic way applicable to a wide range of quantum field theories. It allows the user to define a new physics model and consequently compute its predicted scattering amplitudes with exponential growth of the computing time with process multiplicity rather than factorial growth.Restrictions: There are no built-in restrictions on process complexity.Unusual features: CAMORRA can cope with Majorana fermions.Running time: A ten-gluon amplitude typically takes 9 ms per event.