  We investigate the production of highly energetic top-quark pairs at hadron
colliders, focusing on the case where the invariant mass of the pair is much
larger than the mass of the top quark. In particular, we set up a factorization
formalism appropriate for describing the differential partonic cross section in
the double soft and small-mass limit, and explain how to resum simultaneously
logarithmic corrections arising from soft gluon emission and from the ratio of
the pair-invariant mass to that of the top quark to next-to-next-to-leading
logarithmic accuracy. We explore the implications of our results on approximate
next-to-next-to-leading order formulas for the differential cross section in
the soft limit, pointing out that they offer a simplified calculational
procedure for determining the currently unknown delta-function terms in the
limit of high invariant mass.
