The SMEFTsim package, theory and tools

Abstract

We report codes for the Standard Model Effective Field Theory (SMEFT) in FeynRules -the SMEFTsim package. The codes enable theoretical predictions for dimension six operator corrections to the Standard Model using numerical tools, where predictions can be made based on either the electroweak input parameter set {α ew ,m Z ,Ĝ F } or {m W ,m Z ,Ĝ F }. All of the baryon and lepton number conserving operators present in the SMEFT dimension six Lagrangian, defined in the Warsaw basis, are included. A flavour symmetric U(3) 5 version with possible non-SM CP violating phases, a (linear) minimal flavour violating version neglecting such phases, and the fully general flavour case are each implemented. The SMEFTsim package allows global constraints to be determined on the full Wilson coefficient space of the SMEFT. As the number of parameters present is large, it is important to develop global analyses on reduced sets of parameters minimizing any UV assumptions and relying on IR kinematics of scattering events and symmetries. We simultaneously develop the theoretical framework of a "W-Higgs-Z pole parameter" physics program that can be pursued at the LHC using this approach and the SMEFTsim package. We illustrate this methodology with several numerical examples interfacing SMEFTsim with MadGraph5. The SMEFTsim package can be downloaded at https://feynrules.irmp.ucl.ac.be/wiki/SMEFT.

Benchmarking simplified template cross sections in W H production

“…The higher-dimensional operators are implemented at tree level in the Warsaw basis [2,29] using the SMEFTsim package [37] with the {M W , M Z , G F } input scheme and assuming U (3) 5 invariance in the flavor sector. Because we want to compare the linear dimension-6 contributions with the dimension-6 squared terms, we generate all amplitudes to dimension 6 and do not truncate the cross section.…”

Dijets at Tevatron cannot constrain SMEFT four-quark operators

“…Parton showering was performed by Pythia 8 [42] and Detector simulation was provided by Delphes v.3.4.1 [43]. The relevant SMEFT operators were implemented as a FeynRules model [44] supplied by [45,46]; we chose to utilize the α-scheme for input parameters.…”

Scheming in the SMEFT

“…This corresponds to a scenario in which the new exotic states are too massive to be directly produced or studied at the LHC, but indirect evidence for their presence and properties can emerge in the form of anomalies in measured cross-sections or kinematic distributions. The SMEFT provides a systematic and modelindependent parameterization of these effects, based only on electroweak (EW) scale assumptions: the SMEFT Lagrangian is structured as a series of SU(3) c × SU(2) L × U(1) Y invariant operators constructed out of SM fields 1 and ordered by their canonical dimension d:…”

“…Assuming conservation of the baryon and lepton numbers, the leading beyond-SM effects are described by the Wilson coefficients C i of the dimension-6 operators. There are 59 + h.c. independent structures in L (6) which, assuming an approximate U(3) 5 flavor symmetry among fermion generations, corresponds to a total of 69 independent parameters [1]. Here we adopt the so-called "Warsaw" basis [2] for L (6) and we use a compact notation in which the factor Λ −2 is implicitly absorbed into the definition of the coefficients.…”