How reliably can the Higgs boson mass be predicted from electroweak precision data?

{}From the LEP precision data, upon excluding the observables \Rb, \Rc in a combined fit of the top-quark mass, \Mt, and the Higgs-boson mass, \MH, within the Standard Model, we find the weak 1\si bound of 40\GeV\lsim\MH\lsim 1\TeV. Stronger upper bounds on \MH, sometimes presented in the literature, rely heavily on the inclusion of \Rb in the data sample. Upon including \Rb, the quality of the fit drastically decreases, and \Mt comes out significantly below the experimental value of \Mt=180\pm 12\GeV, thus implying that the stronger bounds are not reliable. Moreover, the stronger bounds on \MH are lost if the deviation between theory and experiment in \Rb is ascribed to contributions of new physics. Replacing \swbar~2(\LEP) by \swbar~2(\SLD) in the data sample leads to the tight bound of \MH\lsim 35\GeV at the 1\si level, which is in conflict, however, with \MH\gsim 65.2\GeV from direct searches.

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12 pages, LaTeX, 1 Postscript figure Report-no: BI-TP 96/06, KA-TP-03-96

electron positron: annihilation
annihilation: electron positron
electroweak interaction: validity test
validity test: electroweak interaction
Higgs particle: mass
mass: Higgs particle
Z0: electroproduction
electroproduction: Z0
Z0: hadronic decay
hadronic decay: Z0

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