=========
OpenLoops
=========

Copyright 2014 Fabio Cascioli, Jonas Lindert, Philipp Maierhoefer, Stefano Pozzorini

Authors

    Fabio Cascioli, cascioli@physik.uzh.ch
    Jonas Lindert, lindert@physik.uzh.ch
    Philipp Maierhoefer, philipp@physik.uzh.ch
    Stefano Pozzorini, pozzorin@physik.uzh.ch

Contact

    openloops@projects.hepforge.org

OpenLoops is a Fortran 90 package for the calculation of tree and one-loop
matrix elements for Standard Model processes based on

    F. Cascioli, P. Maierhoefer and S. Pozzorini,
    Phys. Rev. Lett. 108 (2012) 111601, arXiv:1111.5206

License

    OpenLoops is free software: you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation, either version 3 of the License, or
    (at your option) any later version.

    OpenLoops is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.

    You should have received a copy of the GNU General Public License
    along with OpenLoops.  If not, see <http://www.gnu.org/licenses/>.


============
Installation
============

Requirements

    gfortran 4.6 or later, or ifort
    Python 2.x starting with 2.4
    Apache Subversion (optional, to install from SVN)

You can either download OpenLoops from SVN (recommended)

    svn checkout http://openloops.hepforge.org/svn/OpenLoops/branches/public OpenLoops

or from the OpenLoops web page

    http://www.hepforge.org/downloads

Compile

    cd OpenLoops
    ./scons

Download and compile process libraries

    ./scons auto=<processes>

where <processes> is a comma separated list of the processes or
process collections (ending with "/") which should be installed.
A list of the available process libraries can be found here

    http://openloops.hepforge.org/processes

The set of available processes will be extended continuously.
If you need a process which is not (yet) available, please contact the
OpenLoops authors.


================================================================
Update OpenLoops from SVN (when it's already installed from SVN)
================================================================

To pull updates from SVN and compile

    svn update
    ./scons

To update process libraries (will install new libraries if available and
replace old libraries if newer versions are available)

    ./scons auto=lhc/

After updating OpenLoops, updating the installed processes might be required
for compatibility.


=====================
Support and citations
=====================

Please help us improving OpenLoops by sending feedback to

    openloops@projects.hepforge.org

If you use OpenLoops (or an event sample generated with Sherpa+OpenLoops)
please cite

    F. Cascioli, P. Maierhoefer and S. Pozzorini,
    Phys. Rev. Lett. 108 (2012) 111601, arXiv:1111.5206

In the computation of loop amplitudes, OpenLoops uses CutTools for OPP reduction
and OneLOop to compute scalar integrals (unless other reduction libraries are
installed and used). If you use CutTools and OneLOop please cite

    G. Ossola, C. Papadopoulos, R. Pittau, JHEP 0803 (2008) 042, arXiv:0711.3596
    A. van Hameren, Comput. Phys. Commun. 182 (2011) 2427-2438, arXiv:1007.4716


================
Sherpa+OpenLoops
================

OpenLoops can be used as a plug-in of Sherpa 2.1.0 or later. For the
installation of Sherpa and the usage of Sherpa+OpenLoops please refer to the
Sherpa documentation at

    https://sherpa.hepforge.org

OpenLoops must be enabled by configuring Sherpa with the '--enable-openloops'
option

    ./configure --enable-openloops=</path/to/OpenLoops> [other configure options]
    make
    make install

The OpenLoops installation path can be modified at runtime by setting
(in the Sherpa run card or command line)

    OL_PREFIX=</path/to/OpenLoops>

To run Sherpa in combination with OpenLoops it is sufficient to set the flag

    Loop_Generator=OpenLoops

in the Sherpa runcard. Standard Sherpa+OpenLoops run cards can be found at

    http://openloops.hepforge.org/sherpa-runcards