New physics and the muon anomalous magnetic moment

In this chapter we review various scenarios of physics beyond the Standard Model that may explain the difference between the measured value of the muon anomalous magnetic moment and the Standard Model expectation for this quantity. It was realized long ago that the muon anomalous magnetic moment provides a powerful tool for studying the energy frontier. For example, in late 1950s, the interest in the muon magnetic anomaly was driven by a quest to understand why the muon is heavier than the electron while all other properties of the two leptons are the same. It was suggested that the muon magnetic anomaly is a particular suitable observable since it can be used to probe the validity of QED up to the energy scale of about few GeV, the energy frontier at that time.