Standard Model Effective Theory at NexttoLeadingOrder in QCD
Céline Degrande, Gauthier Durieux, Fabio Maltoni, Ken Mimasu, Eleni Vryonidou & Cen Zhang
A complete implementation of the SMEFT compatible with NLO QCD predictions.
The implementation is based on the Warsaw basis of operators and includes all degrees of freedom consistent with the following symmetry assumptions:
 CPconservation.
 U(2)_{Q} x U(2)_{u} x U(3)_{d} x U(3)_{L} x U(3)_{e} flavor symmetry.
The CKM matrix is approximated as a unit matrix. The flavor symmetry imposes that only the top quark is massive. The model therefore implements the 5flavor scheme for PDFs. The bosonic operators are implemented as in the Warsaw basis employing the M_{Z}, M_{W}, G_{F} scheme of Electroweak input parameters.
The Standard Model input parameters that need to be specified are:
M_{Z}, M_{W}, G_{F}, M_{H}, M_{t}, α_{S}(M_{Z})
The fermionic degrees of freedom (2 & 4 fermion operators) are defined according to the common standards and prescriptions established by the LHC TOP WG for the EFT interpretation of topquark measurements at the LHC (see the dim6top page for more information). This model has been validated at LO with the dim6top implementation.
A new coupling order, NP, is added to the model for the SMEFT interactions. It is assigned through the universal cutoff parameter, Lambda, which takes a default value of 1 TeV^{2} and can be modified along with the Wilson coefficients in the param card.
The definitions.pdf document specifies the operators definitions, normalisations and coefficient names in the UFO model
Usage notes
Restriction cards
Because of the mixture of LO/NLO compatible operators included in the model, restriction cards must be used to access the SMEFT interactions.
Default loading of the model
> import model SMEFTatNLO_U2_2_U3_3_cG_4F_LO_UFO
will load the pure SM without any effective operators.
The LO restriction card should be used when importing the model for LO generation:
> import model SMEFTatNLO_U2_2_U3_3_cG_4F_LO_UFOLO
For NLO QCD generation, the NLO restriction card should be used when importing the model:
> import model SMEFTatNLO_U2_2_U3_3_cG_4F_LO_UFONLO
This invokes a restricted set of operators for which the required counterterms are implemented.
Coupling orders
We recommend specifying the full QCD, QED and NP orders for process generation.
For example:
> generate p p > t t~ QCD=2 QED=0 NP=2 [QCD]
Generates the NLO QCD top pair production process including the QCDinduced SM and the SMEFT contributions.
Excluding operators
We recommend avoiding setting values of Wilson coefficients to 0 when computing at NLO using MadGraph5_aMC@NLO.
Operators should either be removed explicitly with restriction cards or set to a very small nonzero value, e.g., 1e10
Model Files
 SMEFTatNLO_U2_2_U3_3_cG_4F_LO_UFO.tgz : archive of UFO model  4 fermion and c_{G} operators at LO, U(2)^{2} x U(3)^{3} flavor symmetry
Version updates
 2018/12/20  v.0.1: First version upload, 4F and c_{G} operators at LO pending validation; a few minor convention tweaks required to match dim6top exactly. decays.py missing.
 2019/04/03  v.0.1: Added definitions.pdf document and uploaded a new version with a fix for restrict_default.dat
 2019/08/12  v.0.1: Uploaded a new version matching dim6top operator conventions, also some bugfixes and gs normalisation for otG
Attachments (2)

SMEFTatNLO_U2_2_U3_3_cG_4F_LO_UFO.20190812.tgz
(84.6 KB) 
added by kmimasu 3 months ago.
UFO model uploaded 2019/08/12

definitions.pdf
(162.4 KB) 
added by kmimasu 3 months ago.
Operator defintion & normalisation
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