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+<h2>MadGraph 5 Processes</h2>
+
+By far the easiest way to implement new processes into PYTHIA 8 is
+by using the matrix-element generator MadGraph 5. This program has
+an option to output the results of a matrix-element calculation
+as a set of PYTHIA 8 C++ classes (plus further auxiliary code),
+that can then be linked and used as
+<?php $filepath = $_GET["filepath"];
+echo "<a href='SemiInternalProcesses.php?filepath=".$filepath."' target='page'>";?>semi-internal</a> processes,
+meaning they are handled identically with normal internal ones.
+This way, MadGraph 5 can be used to implement processes from
+any model that can be written in terms of a Lagrangian. Any
+<i>2 -> 1</i>, <i>2 -> 2</i> and <i>2 -> 3</i> processes
+can be implemented, the limit being set by the absence of efficient
+phase space generator algorithms for higher multiplicities in
+PYTHIA. Features such as <i>s</i>-channel resonances are
+automatically implemented in the process classes. Besides the process
+library and necessary model files, also an example main program is
+generated for each set of processes, which can be easily modified to
+perform the desired analyses.
+
+<p/>
+In order to create a PYTHIA 8 process library with MadGraph 5, first
+download the MadGraph 5 package from
+<a href="https://launchpad.net/madgraph5" target="page">
+https://launchpad.net/madgraph5</a>, and untar the package. You can
+then specify the location of your <code>pythia81xx</code> directory
+in the file <code>input/mg5_configuration.txt</code>:
+<br/><code>pythia8_path = ./pythia81xx</code>
+<br/>The location can be either relative (to the directory
+<code>MadGraph5_v_x_x_x/.</code>) or absolute.
+
+<p/>
+For any model that is already implemented in the MadGraph 5 package,
+you can directly use the model. Start the MadGraph 5 interface
+<code>bin/mg5</code>, and do:
+<pre>
+import model model_name
+generate your_process_in_mg5_syntax
+add process your_next_process_in_mg5_syntax
+...
+output pythia8 [path_to_pythia81xx_directory]
+</pre>
+
+<p/>
+For examples of MG5 process syntax, please see
+<a href="http://madgraph.phys.ucl.ac.be/EXAMPLES/example_mg5.html"
+target="page">http://madgraph.phys.ucl.ac.be/EXAMPLES/example_mg5.html</a>
+or type <code>help generate</code>. If you specified the path to the
+<code>pythia81xx</code> directory in the <code>mg5_configuration</code>
+file, you do not need to enter it in the <code>output</code> command.
+
+<p/>
+If your preferred model is found on the FeynRules model wiki page,
+<a href="http://feynrules.irmp.ucl.ac.be/wiki/ModelDatabaseMainPage"
+target="page">http://feynrules.irmp.ucl.ac.be/wiki/ModelDatabaseMainPage</a>,
+download the UFO (Universal FeynRules Output) tar file for the model,
+untar in the <code>models/</code> directory, and use as above.
+
+<p/>
+If you want to implement a new model which has not yet been implemented,
+you can do this either using the Mathematica package FeynRules (see
+<a href="http://feynrules.irmp.ucl.ac.be/" target="page">
+http://feynrules.irmp.ucl.ac.be/</a>) or directly edit the UFO model
+files of the most similar model in the <code>models/</code> directory.
+
+<p/>
+The resulting output from the <code>output pythia8</code> command is:
+<ul>
+<li>A process directory <code>Processes_modelname</code> with the
+model information and the files needed for all processes defined for
+this model, placed in the <code>pythia81xx</code> main directory.
+The model files are <code>Parameters_modelname.h/cc</code> and
+<code>HelAmps_modelname.h/cc</code>, and the process files for each
+process class (with the same mass, spin and color of the initial/final
+state particles) are called <code>Sigma_modelname_processname.h/cc</code>.
+The directory also contains a <code>makefile</code> and a model parameter
+file <code>param_card_modelname.dat</code>.</li>
+<li>An example main program in the directory <code>examples/</code>
+(in the <code>pythia81xx</code> main directory) called
+<code>main_modelname_N.cc</code> and a corresponding makefile
+<code>Makefile_modelname_N</code>. This main program links in the
+process classes in the process directory described above. To run the
+example main program, just go to the <code>examples/</code>
+directory and run
+<br/><code>make -f Makefile_modelname_N</code>
+<br/>or run <code>launch</code> directly inside the MadGraph 5
+command line interface.</li>
+</ul>
+
+<p/>
+Note that in order for PYTHIA 8 to be able to automatically decay any
+new particles, it is necessary to specify the branching ratios of the
+particles in the <code>param_card</code> file, see
+[<a href="Bibliography.php" target="page">Ska04,Alw07</a>] for details.
+
+<p/>
+For further technical details, please see the MadGraph 5 release paper
+[<a href="Bibliography.php" target="page">Alw11</a>] and the
+<?php $filepath = $_GET["filepath"];
+echo "<a href='SemiInternalProcesses.php?filepath=".$filepath."' target='page'>";?>semi-internal</a> processes page.
+
+<p/>
+Of course, as with MadGraph 4, MadGraph 5 can also output
+files of parton-level events according to the
+<?php $filepath = $_GET["filepath"];
+echo "<a href='LesHouchesAccord.php?filepath=".$filepath."' target='page'>";?>LHEF</a> standard,
+that can be read in and processed further by PYTHIA 8.
+The advantage is that then the MadGraph 5 phase space generator
+can be used, which opens up for processes with more than three
+particles in the final state. The disadvantages are that it is less
+easy to mix and match with existing PYTHIA processes, and that one
+needs to regenerate and store large LHEF files for different
+kinematics cuts or parameter values.
+
+<p/>
+Please cite the MadGraph 5 release paper [<a href="Bibliography.php" target="page">Alw11</a>] if you use
+MadGraph 5 to generate process libraries for PYTHIA 8.
+
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