Do precision electroweak constraints guarantee e(+)e(-) collider discovery of at least one Higgs boson of a two-Higgs-doublet model?

摘要

We consider a CP-conserving two-Higgs-doublet type II model with a light scalar or pseudoscalar neutral Higgs boson (h = h(0) or h = A(0)) that has no ZZ/WW coupling and, thus, cannot be detected in e(+)e(-) -> Zh (Higgs-strahlung) or <()over bar>nuh (via ww fusion). Despite sum rules which ensure that the light h must have significant tt or bi; coupling, for a wedge of moderate tan beta, that becomes increasingly large as m(h) increases, the h can also escape discovery in both b (b) over barh and t (t) over barh production at a roots = 500-800 GeV e(+)e(-) collider (for expected luminosities.) If the other Higgs bosons happen to be too heavy to be produced, then no Higgs boson would be detected. We demonstrate that, despite such high masses for the other Higgs bosons, only the low-tan beta portion of the no-discovery wedges in [m(h), tan beta] parameter space can be excluded due to failure to fit precision electroweak observables. In the tan beta greater than or similar to 1 regions of the no-discovery wedges, we find that the 2HDM fit to precision electroweak observables has small Delta chi (2) relative to the best minimal one-doublet SM fit. (C) 2000 Elsevier Science B.V. All rights reserved. [References: 17]