Theory of the muon g-2: some recent developments

Aula Bruno Touschek (Laboratori Nazionali di Frascati, Via Enrico Fermi 40, Frascati)

Aula Bruno Touschek

Laboratori Nazionali di Frascati, Via Enrico Fermi 40, Frascati

Via Enrico Fermi 40 00044 Frascati

The anomalous magnetic moment of the muon has served over many decades as an important test of the Standard Model. It is also sensitive to contributions from New Physics around the electroweak scale. Indeed, for the last few years, a discrepancy of more than three standard deviations has been observed between the theoretical prediction in the Standard Model and the measured value. In this talk, we first briefly review the various contributions to the muon g-2 and then focus on recent developments concerning the hadronic contributions which yield the largest uncertainty in the theoretical prediction. We then discuss in detail the hadronic light-by-light scattering contribution. In contrast to the hadronic vacuum polarization correction, this contribution cannot be related to a measurable quantity like a hadronic cross section and therefore one has to rely on models to evaluate it. In order to reduce this model dependence, we present a new QCD short-distance constraint on the numerically dominant pion-exchange contribution and evaluate it in the framework of large N_C QCD. We comment on the status of the other contributions in hadronic light-by-light scattering and give an outlook on how further improvements could be achieved by combining theoretical and experimental constraints on the relevant hadronic form factors. Finally, we present our new estimate for the muon g-2 in the Standard Model.

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