Collinear Divergences at One-loop Order for External Particles in a   Heat-bath
  In hard interactions between external particles incident on a heat-bath, we show that large logarithms are generated when a radiated or absorbed gauge boson is collinear with the initial fermion momentum. These logarithms can be absorbed into process independent splitting/absorption probabilities. Unlike the zero-temperature case, however, they depend explicitly on the temperature and the scale of the interaction. 
Saumen Datta, Sourendu Gupta, V. Ravindran