  Motivated by recent pump-probe experiments we consider the processes by which
"hot" quasiparticles produced near the antinodes of a d-wave superconductor can
relax. We show that in a large region of momentum space processes which break
Cooper pairs are forbidden by energy and momentum conservation. Equilibration
then occurs by scattering with thermal quasiparticles: Umklapp scattering is
exponentially suppressed at low temperatures, but small-angle scattering leads
to power-law behavior. By solving the Boltzmann equation analytically we make
detailed predictions for the temperature and intensity dependence of these
processes, which we compare with experiment.
