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 $SU(2{)}_L\otimes SU(2{)}_R\to SU(2{)}_{L+R}$ with Goldstone bosons, 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 behavior, 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.

• Received 8 January 2013

DOI:https://doi.org/10.1103/PhysRevLett.110.181801