Top quark pair production and decay into six fermions at linear colliders

The production of a \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$t\bar{t}$\end{document} pair and its decay into a six fermion final state of different flavors in \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$e^+e^-$\end{document} annihilation at center of mass energies typical for linear colliders is analyzed in the framework of the standard model. The results of a calculation based on exact matrix elements at the tree level and full six particle phase space are compared with a few different approximations. It is shown that the effects related to off-shellness of the \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$t\bar{t}$\end{document} pair and background contributions are sizable both in the continuum and at the threshold.