\section{Summary and outlook}

In this paper, it has been shown that the measurements of the angular and energy distributions in semi-leptonic ${\rm t\bar t}$ events (${\rm e^+e^- \to t \bar t} \to \ell \nu {\rm q \bar q b \bar b}$) at future ${\rm e^+e^-}$ colliders have a strong potential for a precise determination of the top-quark electroweak couplings.  It has been demonstrated, even with the sole use of these two distributions and modest detector performance, that the lack of incoming beam polarization at the FCC-ee is compensated by the polarization of the final state top quarks, and by a significantly larger integrated luminosity.

Although these projections were obtained with somewhat conservative hypotheses on the detector performance, it will also be important to reproduce the results with a full simulation in a Monte Carlo study, as to further investigate that the detector requirements are indeed quite modest. While the inferred precisions are already competitive with other projects on the market, such a Monte Carlo study will also allow a reliable reconstruction of all observables in the event, beyond the lepton energies and directions, and is expected to bring sizeable improvements, especially on the few remaining correlations between form factors.

The present study is only a first look at this topic for the FCC-ee. It enhances the fantastic potential of a 100-km circular ${\rm e^+e^-}$ collider already envisioned in Ref.~\cite{Bicer_2014} with the full profiling of the top quark from a precise measurement of its electroweak couplings. In view of these new estimates, it becomes of particular interest to check their added value to the sensitivity to new physics, especially when combined with the unequalled precision of the measurements of the Z, the W, and the Higgs boson properties, as well as of the top-quark mass, at the FCC-ee.  