Probing the mechanism of EWSB with a rho parameter defined in terms of Higgs couplings

Abstract

A definition of the rho parameter based on the Higgs couplings with the gauge bosons, rho_h= g_{hWW}}/c^2_W g_{hZZ}, is proposed as a new probe into the origin of the mechanism of electroweak symmetry breaking. While $\rho_h=1$ holds in the SM, deviations from one are predicted in models with extended Higgs sector. We derive a general expresion of rho_h for a model with arbitrary Higgs multiplets, and discuss its size within the context of specific models with Higgs triplets, including the ``Little Higgs'' models recently proposed. We find the even for Higgs models that incorporate the custodial symmetry to make rho=1, one could have rho_h\neq 1, which could be tested at the level of a few percent, with the precision Higgs meassurements expected at the NLC.