Muon $g-2$

Abstract

The story of the anomalous magnetic moment of the muon, $a_{\mu}$, has been a long and absorbing read, with several unexpected plot twists. The theme: is new physics visible in $a_{\mu}$ or not? is clearly an important one. As we head towards what may be the final chapters, the pace of the narrative has quickened and lattice QCD is providing a critical new perspective on some of the key characters. I will review the story so far, focussing on recent episodes but (spoiler alert) depending on your point of view, it may not be heading to a happy ending.