Triviality and the precision bound on the Higgs mass

The triviality of the scalar sector of the standard one-doublet Higgs model implies that this model is only an effective low-energy theory valid below some cut-off scale Lambda. For a heavy Higgs this scale must be relatively low (10 TeV or less). Additional interactions coming from the underlying t heory, and suppressed by the scale Lambda, give rise to model-dependent cor rections to precisely measured electroweak quantities. Dimension six operat ors arising from the underlying physics naturally contribute to the S and T parameters, and their effects should be included in a global fit to the pr ecision data that determines any limit on the Higgs mass. Using dimensional analysis, we estimate the expected size of these corrections in a custodia lly-symmetric strongly-interacting underlying theory. Taking these operator s' coefficients to be of natural size gives sufficiently large contribution s to the T parameter to reconcile Higgs masses as large as 400-500 GeV with the precision data. (C) 1999 Published by Elsevier Science B.V. All rights reserved.