Abstract
For a long time, global fits of the electroweak sector of the standard model (SM) have been used to exploit measurements of electroweak precision observables at lepton colliders (LEP, SLC), together with measurements at hadron colliders (Tevatron, LHC) and accurate theoretical predictions at multi-loop level, to constrain free parameters of the SM, such as the Higgs and top masses. Today, all fundamental SM parameters entering these fits are experimentally determined, including information on the Higgs couplings, and the global fits are used as powerful tools to assess the validity of the theory and to constrain scenarios for new physics. Future measurements at the Large Hadron Collider (LHC) and the International Linear Collider (ILC) promise to improve the experimental precision of key observables used in the fits. This paper presents updated electroweak fit results using the latest NNLO theoretical predictions and prospects for the LHC and ILC. The impact of experimental and theoretical uncertainties is analysed in detail. We compare constraints from the electroweak fit on the Higgs couplings with direct LHC measurements, and we examine present and future prospects of these constraints using a model with modified couplings of the Higgs boson to fermions and bosons.
Highlights
Full fermionic two-loop calculations have become available for the partial widths and branching ratios of the Z boson [10]
In this paper we present an update of the global electroweak fit performed at the two-loop level,1 including a detailed assessment of the impact of the remaining theoretical uncertainties
This benchmark model uses the explicit assumption that no other new physics is present, e.g., there are no additional loops in the production or decay of the Higgs boson and no invisible Higgs decays and undetectable contributions to its decay width
Summary
Full fermionic two-loop calculations have become available for the partial widths and branching ratios of the Z boson [10]. These new calculations improve the theoretical precision and allow for a more meaningful estimate of the theoretical uncertainties due to missing higher perturbative orders. In this paper we present an update of the global electroweak fit performed at the two-loop level, including a detailed assessment of the impact of the remaining theoretical uncertainties. The coming years should lead to progress in the calculation of multi-loop corrections to these observables, as well as to an improved determination of the hadronic contribution to the fine-structure constant evaluated at the Z boson mass scale, αhad The latest results of the global electroweak fit are compared with the expectations for the Phase-1 LHC2 and
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