  Infrared divergences of QCD scattering amplitudes can be derived from an
anomalous dimension matrix, which is also an essential ingredient for the
resummation of large logarithms due to soft gluon emissions. We report a recent
analytical calculation of the anomalous dimension matrix with both massless and
massive partons at two-loop level, which describes the two-loop infrared
singularities of any scattering amplitudes with an arbitrary number of massless
and massive partons, and also enables soft gluon resummation at
next-to-next-to-leading-logarithmic order. As an application, we calculate the
infrared poles in the q qbar -> t tbar and gg -> t tbar scattering amplitudes
at two-loop order.
