  Recent years have seen a significant advance in our ability to calculate
two-loop matrix elements. In this talk we describe an application of this
breakthrough to improve our understanding of the background to the search for a
light Higgs boson at the LHC. In particular, we focus on the QCD corrections to
the gluon fusion subprocess gg to gamma gamma, which forms an important
component of the background in the di-photon channel. We find that the K factor
for this subprocess is significantly smaller than estimated previously.
