Nlc ∗

We demonstrate that the process e + e − → tth at the NLC provides a powerful tool for extracting the tt (Yukawa) couplings of the h. In combination with the e + e − → Zh process , an accurate determination of the ZZ coupling of the h is also possible. The resulting ability to distinguish different models of the Higgs sector is illustrated by detailed studies for two-Higgs-doublet models. In extensions of the Standard Model (SM) there are multiple neutral Higgs bosons. Their masses and couplings are often dependent upon many parameters; CP-violating mixing of CP-even with CP-odd neutral Higgs fields is generally possible. Thus, if Higgs boson(s) exist and are discovered at future colliders, it will be extremely important to determine both the magnitude and the CP nature of their couplings[1, 2, 3]. It has been shown that the process e + e − → tth (h is our notation for a generic neutral Higgs boson) at the proposed Next Linear Collider (NLC) can provide rather accurate determinations of the CP-even and CP-odd tth Yukawa couplings and at least a rough value for the ZZh coupling [3]. The e + e − → Zh process provides a direct measurement of the ZZh coupling when analyzed in the missing-mass mode with Z → e + e − , µ + µ −. Here, we demonstrate that the accuracy with which the couplings can be determined using these two processes will discriminate in a very decisive manner between different models for the Higgs bo-son sector. By way of illustration, we will consider the general Two-Higgs-Doublet Model (2HDM), for which the masses and couplings of the three neutral Higgs bosons are all free parameters. For simplicity, we focus on the h that is the lightest of the three eigenstates, and assume that it is sufficiently light compared to the other two that e + e − → tth is not sensitive to the other Higgs states.