Top physics at CLIC and ILC

Abstract: Measurements of top quark production at $e^+e^-$ colliders can provide a leap in precision in our knowledge of top quark properties and open a new window on physics beyond the Standard Model. In this contribution the top quark physics prospects of linear colliders is reviewed. Progress in detailed full-simulation studies is reported for the highlights of the program. We present the prospects for a measurement of the top quark mass and width in a scan of the beam energy through the pair production threshold, and discuss new studies of alternative measurements in continuum production, which are also capable of a precise determination of the mass in a rigorously defined mass scheme. A precision of 50 MeV on the $\overline{MS}$ mass is expected when taking into account the dominant systematic uncertainties. Another key measurement is the study of the top quark couplings to electroweak gauge bosons, where form factors can be determined to 1% precision, an order of magnitude better than those from the full LHC program. New results extend the prospects to different center-of-mass energies and to CP violating form factors. Finally, new studies are presented indicating the possibility to detect Flavour Changing Neutral Current decays of the top quark at linear colliders, such as the decay $t \rightarrow cH$, to a branching ratio of $BR(t\rightarrow cH) \sim 10^{-5}$.