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

We examine how accurately the general HZV couplings, with $V=Z,\gamma$ , may be determined by studying $e^+e^-\to Hf\bar{f}$ 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 HZV 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 HZZ couplings are generally found to be well constrained, even without these options, while the $HZ\gamma$ couplings are not. The constraints on the latter may be significantly improved by beam polarization.