Where is the Higgs boson?

Abstract

Electroweak precision measurements indicate that the standard model Higgs boson is light and that it could have already been discovered at LEP 2, or might be found at the Tevatron Run 2. In the context of a TeV^-1 size extra dimensional model, we argue that the Higgs boson production rates at LEP and the Tevatron are suppressed, while they might be enhanced at the LHC or at CLIC. This is due to the possible mixing between brane and bulk components of the Higgs boson, that is, the non-trivial brane-bulk `location' of the lightest Higgs. To parametrize this mixing, we consider two Higgs doublets, one confined to the usual space dimensions and the other propagating in the bulk. Calculating the production and decay rates for the lightest Higgs boson, we find that compared to the standard model (SM), the cross section receives a suppression well below but an enhancement close to and above the compactification scale M_c. This impacts the discovery of the lightest (SM like) Higgs boson at colliders. To find a Higgs signal in this model at the Tevatron Run 2 or at the LC with sqrt(s)=1.5 TeV, a higher luminosity would be required than in the SM case. Meanwhile, at the LHC or at CLIC with sqrt(s) ~ 3-5 TeV one might find highly enhanced production rates. This will enable the latter experiments to distinguish between the extra dimensional and the SM for M_c up to about 6 TeV.