NNLL top-antitop production at threshold

We present an update to the NNLL RG-improved QCD prediction of top-antitop production in electron-positron annihilation at threshold. It includes for the first time a complete NNLL resummation of ultrasoft logarithms, which are dominant at this order and give a sizable correction. The renormalization scale dependence of the total resonance cross section decreases substantially compared to earlier predictions, where the ultrasoft logarithms were included only partially.