Scheming in the SMEFT

Abstract

We discuss the constraints on the Standard Model Effective Field Theory inferred from global fits to electroweak data. Special attention is paid to two unconstrained combinations of Wilson coefficients that are present when the analysis is restricted to measurements ofψψ →ψψ scatterings. We illustrate how these unconstrained directions arise due to a reparameterization invariance that characterizesψψ →ψψ processes but is not respected inψψ →ψψψψ scatterings. This invariance is independent of the operator basis adopted and of the choice of the input parameters. This is verified comparing the results obtained in the {α em ,m Z ,Ĝ F } input scheme with those of a {m W ,m Z ,Ĝ F } scheme.

SMEFTsim 3.0 -- a practical guide

“…(2.18) shows that the contributions from Q HW , Q HB , Q HG are fully reabsorbed in the definition of the fields and gauge couplings. As a consequence, these operators have no physical impact in the pure gauge sector, and they only contribute to Higgs-gauge interactions [60]. On the other hand, the operator Q HW B introduces net modifications of all γ and Z couplings.…”

“…In Sections 4.2, 4.3 these formulas are applied to the Warsaw basis case, to recover the known tree-level results, see eg. [1,2,45,49,60,73,74]. Aspects specific to the NLO case have been discussed in [48,50,51,53,75,76].…”

“…The latter generally stem from field or parameter redefinitions in the Lagrangian 9. Ref [60]. used the notation ḡi → ĝi + δgi from Ref [49]…”