ExportUFO
ExportUFO[lag]
computes the Feynman rules for the given Lagrangian lag and generates the corresponding UFO files.
Details and Options
- The ExportUFO routine is the main function when creating a UFO model using Matchete. The workflow of generating UFO files for a given model consists of three main parts:
- Define coupling orders (e.g. QED, QCD, NP), see DefineCouplingOrder.
- Create parameter sheet as a JSON file (create template with DefaultParamCard).
- Invoke the ExportUFO routine.
- For ExportUFO to work properly, both of the two first steps need to be done, before invoking ExportUFO.
- The following options can be given:
-
Legs All Determines the number of external legs that should be considered. Particularly for higher-dimensional EFTs one might want to limit this function to 4 external legs to save computation time. Apart from the default All, the allowed values are positive integers (inclusive), or a list with a single positive integer entry (exclusive). "ExternalMomentum" "outgoing" This option allows to control the direction of the external momenta. The allowed values are "outgoing" (default) and "incoming". Note that MadGraph requires outgoing momenta, which is opposite to the actual definitions of the UFO format using incoming momenta. To comply with the MadGraph definitions, Matchete also defaults to outgoing momenta in ExportUFO. However, note that FeynmanRules uses the opposite default "ExternalMomentum""incoming". "FermionFlow" "DEHK" This option determines how fermionic Feynman rules are determined. By default the algorithm based on the fermion flow and developed by Denner, Eck, Hahn, and Kublbeck (Phys.Lett.B 291 (1992) 278-280) ("DEHK") is used, where the Grassmannian minus signs are neglected and charge conjugation matrices are dropped, which is required when running MadGraph. Note that FeynmanRules uses instead the standard textbook conventions by default "FermionFlow""Standard". "IncludeD4Vanishing" False This option allows to control whether operator structures vanishing in 4 spacetime dimensions should be included in the UFO files generated. By default these structures are removed before the export since their presence can lead to compiler issues in MadGraph. "σNormalization" /4 This option allows to define the normalization of the σμν=n[γμ,γν] Dirac matrices, where n is the provided option value. By default n=/4 is used to comply with MadGraph conventions. Note that the internal Matchete convention is n=/2, which is only changed for the export to the UFO format. Gauge Automatic By default the Rξ/Feynman gauge is used for exporting the Feynman rules to the UFO format. The restriction from general Rξ gauge to Feynman gauge (ξ=1) is achieved through the option Rξ. The allowed values are Automatic, Manual, Rξ, and Unitary. Rξ 1 Sets all gauge parameters to unity (ξ=1) , thus restricting to Feynman gauge for the vector fields that have not been fixed to unitary gauge before. Note that MadGraph can still use the resulting UFO files for unitary gauge simulations, by internally switching the propagators and neglecting Goldstone bosons. The allowed values are 1 (default) and General. FeynmanRules None If None (default) is given, ExportUFO will derive the Feynman rules automatically. Alternatively, one can also provide here an association containing the Feynman rules, to be included in the UFO, that was previously determined using FeynmanRules. The format of this association needs to match the output format of FeynmanRules. Note in particular, that FeynmanRules uses different default values for the options "ExternalMomentum" and "FermionFlow" compared to ExportUFO. Consistency has to be ensured by the user in this case. DefaultValues False If set to True, default values for the SM input parameters will be included and automatically assigned to the model parameters. This is only allowed when InputFileNone is used as option. This feature only serves as help for simple models and might not work in more complicated scenarios. InputFile None This option allows to specify the path to a parameter input file using the JSON format. If None is given (default) then the default parameter card will be used. This is highly discouraged as one will have to edit the UFO files manually afterwards. A template for the parameter card can be generated automatically using DefaultParamCard. FlavorInvariants <> Allows to specify flavor invariants that are used to parametrize the couplings. The flavor invariants provided should follow the format of the output of ImposeFlavorSymmetry. This option can only be given if InputFile None is used, otherwise, the flavor invariants have to be provided directly to DefaultParamCard. OutputDirectory Automatic This option allows to specify the output directory where the UFO files should be saved. By default a new directory, named "UFO_output", will be created in the current working directory, which can be found using Directory[]. Information "author""Matchete","model_version""0.0","arxiv""0000.00000" Allows to specify additional information (such as an author name, version number, and paper reference) to be included in the head of the UFO files. Verbose True Can be set to False to suppress auxiliar printing statements.
Examples
open allclose allBasic Examples (1)
As an illustrative example we will generate the UFO files for the SM. First, we can load the SM and perform electroweak symmetry breaking:
Next, we define the appropriate coupling orders for QED and QCD:
We can then export the UFO files using
Since no parameter card was specified as InputFile, an interactive window will open where the one can modify the exported parameter. The resulting UFO files will be stored in the default location, which is the sub-directory "UFO_output" of the current working directory (Directory[]).
Since the Lagrangian was not gauge fixed before (using the function GaugeFixLagrangian), the gauge fixing is performed automatically and Matchete informs the user about choosing Feynman gauge as default. This choice can be overwritten using the Gauge and Rξ options.
Options (9)
Legs (1)
"FermionFlow" (1)
Use text book conventions for deriving Feynman rules:
do not use the resulting UFO file with MadGraph as it will produce wrong results! For more details see the documentation of FeynmanRules. By default ExportUFO uses "FermionFlow""DEHK" following the algorithm introduced by Denner, Eck, Hahn, and Kublbeck (Phys.Lett.B 291 (1992) 278-280), which is used by MadGraph as well.
Gauge (1)
By default ExportUFO uses the Rξ/Feynman gauge for exporting the Feynman rules.
Rξ (1)
By default ExportUFO sets all gauge parameters to unity (ξ=1) for exporting the Feynman rules. Generic gauge parameters can be retained using the option RξGeneral. Note that the general Rξ gauge implementation in the UFO format is currently only gauge invariant in the zero-width limit for the vectors and Goldstones.
FeynmanRules (1)
One can manually compute the Feynman rules in unitary gauge:
and then pass them to the UFO export:
One should make sure that the "FermionFlow", "ExternalMomentum", and Gauge options are chosen consistently between ExportUFO and FeynmanRules, and the event generator used later on.
DefaultValues (1)
See the documentation of DefaultParamCard.
InputFile (1)
The default parameter card for a given Lagrangian can be generated using:
This parameter card contains a minimal parametrization of all couplings and can be modified manually before loading it with ExportUFO:
OutputDirectory (1)
Neat Examples (1)
Flavor symmetries can be implemented in the UFO through the parameter card. For details see the documentation of DefaulParamCard, ImposeFlavorSymmetry, and the tutorials From BSM to EFT: Feynman Rules and UFO and SMEFT: Feynman Rules and UFO.