Composite resonances and their impact on the EW chiral Lagrangian

Abstract

In this talk we study the low-energy effective couplings generated by strongly-coupled electroweak models that contain heavy composite resonances. Invariance under $SU(2)_L\times SU(2)_R$ is a key ingredient in the construction of the resonance action. For simplicity, in these proceedings we focus our attention on the impact of a heavy colourless vector V, which transforms as a triplet under the custodial group. More precisely, we study the couplings that are relevant for the vector form-factors of the L+R current into two electroweak Goldstones and into two Standard Model fermions, which contribute to the oblique parameters S and T and the anomalous $Z\to f\bar{f}$ couplings, respectively. Our predictions are compatible with bounds from direct and indirect searches for Mv > 1.5 TeV. Finally, although we consider an antisymmetric tensor formalism to describe the vector resonance, we derive the equivalent action in the Proca four-vector representation and show that the predictions for low-energy couplings and form-factors are identical, as expected.