Limits on a composite Higgs boson

Precision electroweak data are generally believed to constrain the Higgs bo son mass to lie below approximately 190 GeV at 95% confidence level. The st andard Higgs model is, however, trivial and can only be an effective field theory valid below some high energy scale characteristic of the underlying nontrivial physics. Corrections to the custodial isospin violating paramete r T arising from interactions at this higher energy scale dramatically enla rge the allowed range of Higgs mass. We perform a fit to precision electrow eak data and determine the region in the (m(H), Delta T) plane that is cons istent with experimental results. Overlaying the estimated size of correcti ons to T arising from the underlying dynamics, we find that a Higgs mass up to 500 GeV is allowed.