deletions | additions       diff --git a/Introduction.tex b/Introduction.tex  index e1165fb..e285eb1 100644  --- a/Introduction.tex  +++ b/Introduction.tex 
...
The design study of Future Circular Colliders (FCC) in a 100-km ring in the Geneva area has started at CERN at the beginning of 2014, as an option for a post-LHC particle accelerators. The study has an emphasis on proton-proton and electron-positron high-energy frontier machines. The first step of the physics programme would make use of an ${\rm e^+e^-}$ collider, called FCC-ee and formerly known as TLEP, with centre-of-mass energies ranging from the Z pole to the ${\rm t\bar t}$ threshold and beyond. A first look at the physics case of the FCC-ee can be found in Ref.~\cite{Bicer_2014}.  The only aspect of the top-quark physics alluded to summarized  in this first look concerns the precision measurements of the top-quark mass, width and Yukawa coupling through a scan of the ${\rm t\bar t}$ production threshold, with $\sqrt{s}$ comprised between~340 and~350\,GeV. The expected precision of top-quark mass is in turn used in a global electroweak fit to set constraints on new physics coupled to gauge bosons up to a scale of 100\,TeV. Although not alluded to in the first look, new physics might also show up through deviations of the top-quark couplings to gauge bosons with respect to their standard-model predictions. Theories in which the top-quark and the Higgs boson are composite would lead to such deviations. While these theories also lead to modifications of the Higgs boson couplings and of the Z decay width, it is not unlikely that the inclusion of a direct measurement of the ttZ coupling in the global electroweak fit further constrain these theories. It is widely believed (see, e.g., Ref.~\cite{Baer_2013}) that both a centre-of-mass energy well beyond the top-quark pair production threshold and a large longitudinal polarization of the incoming electron and positron beams are crucially needed to disentangle the tt$\gamma$ and the ttZ couplings, through the measurements of the total event rate and the forward-backward asymmetry of the top quark. In this short letter, however, the sensitivity to the top-quark electroweak couplings is estimated with an optimal-observable analysis of the lepton angular and energy distributions from ${\rm t\bar t}$ production in the $\ell \nu {\rm q \bar q b \bar b}$ final states at the FCC-ee, {\it i.e.}, without incoming longitudinal beam polarization and with a centre-of-mass energy not significantly above the ${\rm t\bar t}$ production threshold.