Prospects of measuring general Higgs couplings at e⁺e^- linear colliders

We examine how accurately the general HΖV couplings, with V = Ζ, γ, may be determined by studying e⁺e^- → Hff̄ processes at future e⁺e^- linear colliders. By using the optimal-observable method, which makes use of all available experimental information, we find out which combinations of the various HΖV coupling terms may be constrained most efficiently with high luminosity. We also assess the benefits of measuring the tau-lepton helicities, identifying the bottom-hadron charges, polarizing the electron beam and running at two different collider energies. The HΖΖ couplings are generally found to be well constrained, even without these options, while the HΖγ couplings are not. The constraints on the latter may be significantly improved by beam polarization.