Flavourful SMEFT likelihood for Higgs and electroweak data

Abstract

We perform an updated fit to LHC Higgs data and LEP electroweak precision tests in the framework of the Standard Model Effective Field Theory (SMEFT). We assume a generic structure of the SMEFT operators without imposing any flavour symmetries. The implementation is released as part of the public global SMEFT likelihood. This allows one to fit parameters of a broad class of new physics models to combined Higgs, electroweak, quark flavour, and lepton flavour observables. I. INTRODUCTIONAfter the discovery of the 125 GeV boson [1,2], the Higgs searches at the LHC have turned into precision tests of the Standard Model (SM). The SM predicts the coupling strength between each fundamental particle and the Higgs in terms of that particle's mass, without any adjustable parameters. Beyond the SM (BSM), however, these couplings can be modified, therefore measurements of Higgs production cross sections and decay rates may reveal the fundamental theory underlying the SM. It is beneficial to describe Higgs coupling modifications in the model-independent language of effective field theory (EFT) [3][4][5]. Assuming new physics decouples, that is to say the masses of non-SM particles are parametrically larger than the weak scale, the relevant effective theory at energies E ∼ m h ≈ 125 GeV is the so-called SMEFT. That theory has the same particle content and local symmetry as the SM, but it admits interaction terms (operators) in the Lagrangian with canonical dimensions larger than four. The Higgs data can be interpreted as constraints on Wilson coefficients of the higher-dimensional operators.Advantages of the SMEFT are not restricted to LHC Higgs physics. The theory offers a universal framework to describe a vast spectrum of precision measurements performed in weak scale colliders such as the LHC, Tevatron, or LEP. In particular, it is a perfect language to describe the so-called electroweak precision tests, that is accurate measurements of Z and W boson properties. A straightforward observation is that SMEFT operators may simultaneously affect both Higgs and electroweak observables. Therefore it makes sense to combine the two sets in order to increase the constraining power of data [6][7][8][9][10][11][12][13][14][15][16]. This work represents another step forward in this direction.In this paper we construct a likelihood for Wilson coefficients of dimension-6 SMEFT operators using a large set of Higgs and electroweak observables. Compared to previous analyses, the main novelties are:1. We do not impose any simplifying assumptions about the flavour structure of dimension-6 operators. This makes the analysis considerably more difficult, but the advantage is that our results are more general. The likelihood we provide can thus be used to constrain a variety of BSM models [17] beyond the U (3) 5 or minimal flavour violation paradigm. In particular, it can be applied to models addressing the so-called b → s anomalies [18,19], which must always involve a highly non-trivial flavour structure.2. All code employed for our analysis is o...

Putting standard model EFT fits to work

“…The importance of the assumptions about flavor in the results of the global fits has been emphasized in Refs. [2,18].…”

The impact of flavour data on global fits of the MFV SMEFT

“…A likelihood for general flavour structures, including Higgs and electroweak observables, was recently calculated in ref. [88]. Processes involving FCNCs will now depend on both flavour-violating operators at tree level and flavour-conserving operators at loop level.…”

Flavour symmetries in the SMEFT

“…9) Thus all the hermitian structures in the category B) yield three CP-even couplings. Finally, for the operators in the category C) only two contractions are possible, such as 10) and similarly for the u fields. All other contractions either reduce to those or to genuine singlet contractions that have already been counted in the U(3) 5 invariant case.…”

“…neglecting terms with different helicity. 10 Separating up and down quark components of F τ q , as well as SU(2) L singlet and triplet components of Σ q , we can write…”

“…See e.g [6][7][8][9][10][11][12]. for recent reviews and phenomenological analyses of the SMEFT with special emphasis on flavour observables.…”