A Monte Carlo global analysis of the Standard Model Effective Field Theory: the top quark sector

Abstract

We present a novel framework for carrying out global analyses of the Standard Model Effective Field Theory (SMEFT) at dimension-six: SMEFiT. This approach is based on the Monte Carlo replica method for deriving a faithful estimate of the experimental and theoretical uncertainties and enables one to construct the probability distribution in the space of the SMEFT degrees of freedom. As a proof of concept of the SMEFiT methodology, we present a first study of the constraints on the SMEFT provided by top quark production measurements from the LHC. Our analysis includes more than 30 independent measurements from 10 different processes at √ s = 8 and 13 TeV such as inclusive tt and single-top production and the associated production of top quarks with weak vector bosons and the Higgs boson. State-of-the-art theoretical calculations are adopted both for the Standard Model and for the SMEFT contributions, where in the latter case NLO QCD corrections are included for the majority of processes. We derive bounds for the 34 degrees of freedom relevant for the interpretation of the LHC top quark data and compare these bounds with previously reported constraints. Our study illustrates the significant potential of LHC precision measurements to constrain physics beyond the Standard Model in a model-independent way, and paves the way towards a global analysis of the SMEFT.

Consistency of the standard model effective field theory

“…The bounds derived in this work demarcate the space of experimentally accessible deviations into those that can be associated with well-defined UV completions and those that cannot. Accordingly, the bounds represent significantly constraining theoretical priors on the SMEFT parameter space, which would be particularly appropriate in the context of global analyses [111,112]. Conversely, any conclusively-measured experimental violation of our bounds would have powerful implications for fundamental assumptions about physics, falsifying low-energy causality/locality, Lorentz invariance, and, by extension, both low-energy quantum field theory and perturbative string theory [67].…”

O new physics, where art thou? A global search in the top sector

“…In this appendix we list the relations between the relevant operators in our analysis and the operators in the Warsaw basis, following the notation of Refs. [21,41]. Using the SU (2) and SU (3) identities τ I ij τ I kl = −δ ij δ kl + 2δ il δ jk , T A ab T A cd = − 1 6 δ ab δ cd + 1 2 δ ad δ bc , and the Fierz identities for anti-commutating fermion fields, (qγ µ q)(Qγ µ Q) = (qγ µ Q)(Qγ µ q), (ūγ µ u)(tγ µ t) = (ūγ µ t)(tγ µ u),…”

“…Its biggest success has been the application to Higgs and electroweak boson measurements at the LHC [8][9][10][11][12][13]. Most recently, the same approach [14][15][16] has been used to systematically analyze top quark measurements at the LHC [17][18][19][20][21] and at future colliders [22,23] and their link to bottom sector [24]. These efforts pave the way towards a global SMEFT analysis at the LHC.…”

Electroweak and QCD corrections to Z and W pole observables in the standard model EFT

“…A program of calculations has begun to treat the SMEFT contributions at NLO, for both the QCD and electroweak (EW) contributions. The SMEFT QCD corrections to gauge boson pair production [11,12] and top quark production and decay [13][14][15][16] are known. The electroweak SMEFT corrections to Higgs decays to bb [17][18][19], γγ [20][21][22][23], Zγ [24,25], ZZ [24], and W W [20] have also been computed, along with partial corrections to the Drell Yan process [26].…”