Lepton Magnetic Moments: What They Tell Us

TL;DR

Recent precise measurements of the muon g-2, combined with advanced lattice QCD calculations, have reinforced the Standard Model's validity, reducing previous discrepancies and challenging the need for new physics explanations.

Contribution

The paper highlights the impact of improved lattice QCD calculations on muon g-2 theory, aligning it more closely with experimental results and diminishing signs of beyond Standard Model physics.

Findings

Lattice QCD results increased the hadronic contributions, reducing the theory-experiment gap.

The discrepancy between dispersive and lattice results can be explained by rho-gamma mixing corrections.

The Standard Model now appears more consistent with muon g-2 measurements, challenging previous BSM indications.

Abstract

Recently, the exciting new Fermilab (FNAL) Muon g-2 measurement impressively confirmed the final Brookhaven (BNL) result from 2004, and with a result four times more precise, has launched a new serious attack on the Standard Model (SM). On the theoretical side, ab initio lattice QCD (LQCD) calculations of hadronic vacuum polarization have made remarkable progress. They are now the new standard for studying the leading non-perturbative contributions, which have previously hindered matching with the precision required for full exploitation of the experimental results. The lattice results affected both leading hadronic contributions the hadronic vacuum polarization (HVP) and the hadronic light-by-light (HLbL) contributions by increasing the previously generally accepted $e^+e^-$ to hadrons based dispersion relation results. The shifts reduced the discrepancy between theory and experiment, leaving nothing missing. One of the most prominent signs of Beyond the Standard Model (BSM) physics has disappeared: the SM appears validated more than ever, in agreement with what other searches at the Large Hadron Collider (LHC) at CERN tell us! A triumph of the SM, even though the SM cannot explain known cosmological puzzles like dark matter or baryogenesis, and why neutrino masses are so tiny, the absence of strong CP violation, for example. I also argue that the discrepancy between the data-driven dispersive result and the lattice QCD results for the hadronic vacuum polarization can be largely explained by correcting the $e^+e^-$ data for 'rho-gamma' mixing effects.