Top quark pair production and decay near threshold in e+e- collisions

We review the physics involved in the production and decay of top quarks in e+e-→t(anti)t near threshold, with special emphasis on the recent theoretical study on the decay process of top quarks in the threshold region. The energy-angular distribution of l+ in semileptonic top decays is calculated including the full O(αs) corrections. Various effects of the final-state interactions are elucidated. A new observable is defined near threshold, which depends only on the decay of free polarized top quarks, and thus it can be calculated without bound-state effects or the final-state interactions. (author)