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Two-Higgs-Doublet Models and Enhanced Rates for a 125 GeV Higgs

We examine the level of enhancement that can be achieved in the ZZ and γγchannels for a two-Higgs-doublet model Higgs boson (either the light h or the heavy H) with mass near 125 GeV after imposing all constraints from LEP data, B physics, precision electroweak data, vacuum stability, unitarity and perturbativity. The latter constraints restrict substantially the possibilities for enhancing the gg -> h -> γγor gg -> H -> γγsignal relative to that for the SM Higgs, hSM. Further, we find that a significant enhancement of the gg -> h -> γγor gg -> H -> γγsignal in Type II models is possible only if the gg -> h -> ZZ or gg -> H -> ZZ mode is even more enhanced, a situation disfavored by current data. In contrast, in the Type I model one can achieve enhanced rates in the γγfinal state for the h while having the ZZ mode at or below the SM rate - the largest [gg -> h -> γγ]/[gg -> hSM -> γγ] ratio found is of order ~1.3 when the two Higgs doublet vacuum expectation ratio is tanβ= 4 or 20 and the charged Higgs boson has its minimal LEP-allowed value of m_{H^\pm} = 90 GeV.