Heavy Quarks and Leptons at $e^+e^-$ Colliders
  The production of massive quarks and leptons in $e^+e^-$ collisions is studied using exact helicity amplitudes. Total cross sections as a function of $y_{\rm cut}$, in both the JADE and the $k_T$ algorithms, are presented and compared with massless results. Some invariant mass distributions are examined in relation to Higgs detection. Compact expressions for the helicity amplitudes are given. 
A. Ballestrero, E. Maina and S. Moretti