Incorporating all recent theoretical advances, we resum soft-gluon
corrections to the total ttˉ cross-section at hadron colliders at the
next-to-next-to-leading logarithmic (NNLL) order. We perform the resummation in
the well established framework of Mellin N-space resummation. We exhaustively
study the sources of systematic uncertainty like renormalization and
factorization scale variation, power suppressed effects and missing two- and
higher-loop corrections. The inclusion of soft-gluon resummation at NNLL brings
only a minor decrease in the perturbative uncertainty with respect to the NLL
approximation, and a small shift in the central value, consistent with the
quoted uncertainties. These numerical predictions agree with the currently
available measurements from the Tevatron and LHC and have uncertainty of
similar size. We conclude that significant improvements in the ttˉ
cross-sections can potentially be expected only upon inclusion of the complete
NNLO corrections.Comment: 17 pages, 4 figures. V2 updates tables and figures including results
for sqrt(S)=8 TeV. Version to appear in Phys Lett