Seminar held by Uli Haisch

The decay of the Higgs boson into two photons is a cornerstone process for precision Higgs physics. While the dominant loop contributions from W bosons and top quarks are well understood, recent studies have raised questions about potential hadronic effects from non-perturbative QCD. In this talk, I present a systematic evaluation of these effects using dispersion relations. The analysis shows that hadronic contributions are exceedingly small —altering the decay width by at most about 0.004% — and can safely be neglected, even for future high-precision Higgs measurements. As an aside, I also estimate the possible size of hadronic contributions to Higgs production in gluon-gluon fusion.