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

A definition of the rho-parameter based on the Higgs couplings with the gauge bosons, ρHi≡gHiWW/(gHiZZc2W), is proposed as a new probe into the origin of the mechanism of electroweak symmetry breaking. While ρhSM=1 holds in the standard model, deviations from one for ρHi are predicted in models with extended Higgs sector. We derive a general expression of ρHi 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 sectors that incorporate the custodial symmetry to make ρ=1, one could have ρHi≠1, which could be tested at the level of a few percent, with the precision Higgs measurements expected at the next linear collider (NLC).