Electroweak Precision Observables, New Physics and the Nature of a 126 GeV Higgs Boson

TL;DR

This paper analyzes electroweak precision data in the Standard Model with a 126 GeV Higgs, incorporating new physics effects and deriving constraints on various parameters and operators.

Contribution

It introduces a comprehensive, model-independent fit of electroweak observables including new physics contributions and bounds on dimension-six operators.

Findings

Composite Higgs models are strongly constrained.

Bounds on S, T, U and epsilon parameters are established.

Constraints on modified Higgs couplings and dimension-six operators are derived.

Abstract

We perform the fit of electroweak precision observables within the Standard Model with a 126 GeV Higgs boson, compare the results with the theoretical predictions and discuss the impact of recent experimental and theoretical improvements. We introduce New Physics contributions in a model-independent way and fit for the S, T and U parameters, for the $\epsilon_{1,2,3,b}$ ones, for modified $Zb\bar{b}$ couplings and for a modified Higgs coupling to vector bosons. We point out that composite Higgs models are very strongly constrained. Finally, we compute the bounds on dimension-six operators relevant for the electroweak fit.