Viability of strongly-coupled scenarios with a light Higgs-like boson

TL;DR

This paper calculates the oblique parameters S and T in strongly-coupled electroweak models with a light Higgs, showing that experimental constraints imply heavy resonance states and a Higgs coupling close to the Standard Model.

Contribution

It provides a next-to-leading order calculation of S and T using an effective Lagrangian with resonance states, applicable to composite Higgs models.

Findings

Resonance masses are constrained to be above the TeV scale.

Higgs-like scalar's WW coupling is close to the Standard Model.

Results are generic for strongly-coupled electroweak symmetry breaking models.

Abstract

We present a one-loop calculation of the oblique S and T parameters within strongly-coupled models of electroweak symmetry breaking with a light Higgs-like boson. We use a general effective Lagrangian, implementing the chiral symmetry breaking SU(2)_L x SU(2)_R -> SU(2)_{L+R} with Goldstones, gauge bosons, the Higgs-like scalar and one multiplet of vector and axial-vector massive resonance states. Using a dispersive representation and imposing a proper ultraviolet behaviour, we obtain S and T at the next-to-leading order in terms of a few resonance parameters. The experimentally allowed range forces the vector and axial-vector states to be heavy, with masses above the TeV scale, and suggests that the Higgs-like scalar should have a WW coupling close to the Standard Model one. Our conclusions are generic and apply to more specific scenarios such as the minimal SO(5)/SO(4) composite Higgs model.