Radiative improvement of spin and Darwin terms in the NRQCD action
  We present updated results for the radiative improvement of the \sigma.B term and the spin-dependent four-fermion terms in the lattice NRQCD action, and first results for the radiative corrections to the NRQCD Darwin term and spin-independent four-fermion terms. The spin-dependent terms have significant impact on getting the correct hyperfine splitting for both bottomonium and heavy-light mesons, while the spin-independent terms suffer from a conspiracy between lattice artifacts and severe IR divergences that complicates their evaluation. 
T. C. Hammant, A. G. Hart, G. M. von Hippel, R. R. Horgan, C. J.   Monahan
hep-lat