The Z decay width in the SMEFT: y t and λ corrections at one loop

Abstract

We calculate one loop y t and λ dependent corrections toΓ Z ,R 0 f and the partial Z widths due to dimension six operators in the Standard Model Effective Field Theory (SMEFT), including finite terms. We assume CP symmetry and a U(3) 5 symmetry in the UV matching onto the dimension six operators, dominantly broken by the Standard Model Yukawa matrices. Corrections to these observables are predicted using the input parameters {α ew ,M Z ,Ĝ F ,m t ,m h } extracted with one loop corrections in the same limit. We show that at one loop the number of SMEFT parameters contributing to the precise LEPI pseudoobservables exceeds the number of measurements. As a result the SMEFT parameters contributing to LEP data are formally unbounded when the size of loop corrections are reached until other data is considered in a global analysis. The size of these loop effects is generically a correction of order ∼ % to leading effects in the SMEFT, but we find multiple large numerical coefficients in our calculation at this order. We use a MS scheme, modified for the SMEFT, for renormalization. Some subtleties involving novel evanescent scheme dependence present in this result are explained.

The SMEFTsim package, theory and tools

“…• The use of anm W input parameter has some advantages when developing one loop results in the SMEFT, see the discussion in Ref. [39,[49][50][51]. In addition, the scales of the input parameters are closer together using {m W ,m Z ,Ĝ F } reducing logarithmic enhancements present in runningα ew for LHC predictions, and related mixing effects with L (6) operators.…”

Matching for FCNC effects in the flavour-symmetric SMEFT

“…Precision electroweak data have been used to develop fits of the relevant subset of operators that contribute to those observables [13][14][15][16][17][18][19]. Loop corrections to very precisely measured and particularly interesting processes have been calculated [20][21][22][23][24][25][26][27][28][29][30][31][32]. LHC searches have also been interpreted in the SMEFT, with techniques to address the unique theoretical errors inherent in high energy searches for EFT effects recently developed [33,34].…”

Dijets at Tevatron cannot constrain SMEFT four-quark operators

“…Much foundational work has gone into the SMEFT, enabling the sorts of analyses presented here. A complete basis of operators [6] and their renormalization behavior [7][8][9] are known, and significant effort has been invested in precision electroweak studies [10][11][12][13][14][15][16] and loop calculations of observables relevant to both electroweak data and hadron collider searches [17][18][19][20][21][22][23][24][25][26][27][28][29][30]. The ultimate goal of all this effort is a global fit of all the data in terms of NP scale and Wilson coefficients, with which it will be possible to test any UV model, including those that haven't yet been invented, against the precise measurements made at the LHC and earlier experiments.…”