Flavourful SMEFT likelihood for Higgs and electroweak data

Adam Falkowski,David Straub

doi:10.1007/jhep04(2020)066

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.

Highlights

In this paper we construct a likelihood for Wilson coefficients of dimension-6 Standard Model Effective Field Theory (SMEFT) operators using a large set of Higgs and electroweak observables
In this paper we construct a likelihood for Wilson coefficients of dimension-6 SMEFT operators using a large set of Higgs and electroweak observables
By the very definition of these observables, any explanation must involve new physics coupling with a different strength to the different lepton generations. Integrating out such new physics leads to the SMEFT with a flavour non-universal structure of dimension-6 operators, which could not be constrained by previous combined Higgs and electroweak fits due to their assumption of flavour universality

Summary

SMEFT framework

We briefly review the SMEFT framework to fix our notation. We consider the extension of the SM by all independent dimension-6 operators Qi invariant under the SM gauge symmetries [29, 30]: LSMEFT = LSM + Ci Qi. In our conventions the Wilson coefficients Ci have dimensions [mass]−2 and they count as O(Λ−2) in the EFT expansion. This is because the electroweak and Higgs observables we are concerned with in this paper are all CP-conserving. The CP-violating operators affect our observables only at the quadratic level in the corresponding Wilson coefficients, at O(Λ−4) in the EFT expansion. We take into account only tree-level effects of dimension-6 operators, except in the observables where the SM contribution itself appears first at one loop. In this approximation, the operators affecting the Higgs and electroweak precision data are shown in table 1. The only four-fermion operator entering is the operator [Qll]1221 that interferes with the SM amplitude in muon decay and modifies the relation between the muon lifetime (defining the Fermi constant GF ) and the electroweak parameters.

Experimental data and fit methodology

Confidence intervals for Wilson coefficients

Oblique parameters

Custodial vector resonance model

Summary