Hadronic light-by-light scattering in the anomalous magnetic moment of the muon.

Hadronic light-by-light scattering in the anomalous magnetic moment of the muon $a_\mu$ is one of two hadronic effects limiting the precision of the Standard Model prediction for this precision observable, and hence the new-physics discovery potential of direct experimental determinations of $a_\mu$. In this contribution, we report on recent progress in the calculation of this effect achieved both via dispersive and lattice QCD methods.