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Manuscript Title: A simple algorithm for automatic Feynman diagram generation
Authors: Bo Xiao, Hao Wang, Shou-hua Zhu
Program title: EasyFeynDiag
Catalogue identifier: AEPD_v1_0
Distribution format: tar.gz
Journal reference: Comput. Phys. Commun. 184(2013)1966
Programming language: C.
Computer: Platforms on which an ANSI C compiler is available.
Operating system: Operating Systems on which an ANSI C compiler is available.
RAM: 900,000 bytes
Keywords: Feynman diagram, Effective theory, Perturbative expansion, Scattering process.
PACS: 12.38.Bx, 12.15.Lk.
Classification: 4.4.

Nature of problem:
Automatic generation of Feynman diagrams from given interactions, scattering process, and number of loops.

Solution method:
The algorithm of EasyFeynDiag is translated from the perturbative expansion formula of the S-matrix. EasyFeynDiag follows an ordered iterative traversing procedure to find all the possible combinations of the fields and creation/annihilation operators. Two selection rules are adopted in turn, to suppress equivalent Feynman diagrams originating from vertices relabelling, and from multiple identical particles in an interaction term, respectively.

Restrictions:
  1. There are default values for the maximum external particles and internal vertices for a scattering process, and maximum legs or leg types for an interaction term. Users need to modify the corresponding values in the code to get larger limits.
  2. Equivalent Feynman Diagrams arise at two-loop or higher order, although this fact does not hurt the correctness of the obtained Feynman amplitudes.

Unusual features:
Allows for arbitrary physical model and arbitrary number of loops. Symmetry factors are naturally generated. Very small. Very fast.

Additional comments:
This program serves mainly as an illustration of the algorithm described in its companion paper.

Running time:
About 0.015 seconds to generate all the Feynman diagrams of a typical two-loop order uubarttbar process in QCD model.