LEP Limits on CP - Violating Non - Minimal Higgs Sectors

We derive a sum rule which shows how to extend LEP limits on the masses of the lightest CP-even and CP-odd Higgs bosons of a CP-conserving two-Higgs-doublet model to any two Higgs bosons of a general CP-violating two-Higgs-doublet model. We generalize the analysis to a Higgs sector consisting of an arbitrary number of Higgs doublets and singlets, giving explicit limits for the CP-conserving and CP-violating two-doublet plus one-singlet Higgs sectors. Models of electroweak symmetry breaking driven by elementary scalar dynamics predict the existence of one or more physical Higgs bosons. One can use LEP data to place significant bounds on Higgs boson masses. The minimal model consists of a one-doublet Higgs sector as employed in the Standard Model (SM), which gives rise to a single CP-even scalar Higgs, h SM. The absence of any e + e − → Zh SM signal in LEP1 data (where the Z is virtual) and LEP2 data (where the Z is real) translates into a lower limit on m h SM which has been increasing as higher energy data becomes available. For example, the latest ALEPH data implies m h SM > ∼ 70.7 GeV [1]. Ultimately, the strongest limit will be obtained by combining the ALEPH data with similar results from the L3, OPAL and DELPHI experiments. The simplest and most attractive generalization of the SM Higgs sector is a two-Higgs-doublet model (2HDM), the CP-conserving version of which has received considerable attention, especially in the context of the minimal supersymmetric model (MSSM) [2]. A CP-conserving two-Higgs-doublet model predicts the existence of two neutral CP-even Higgs bosons (h 0 and H 0 , with m h 0 ≤ m H 0), one neutral CP-odd Higgs (A 0) and a charged Higgs pair (H ±). The negative results of Higgs boson searches at LEP can be formulated as restrictions on the parameter space of this and more general Higgs sector models. For the most general CP-conserving two-doublet model one can 1