The anomalous magnetic moment of the muon in the Standard Modelстатья
Статья опубликована в высокорейтинговом журнале
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Дата последнего поиска статьи во внешних источниках: 8 января 2021 г.
Аннотация:We review the present status of the Standard Model calculation of the anomalous magnetic moment of the muon.This is performed in a perturbative expansion in the fine-structure constant alpha and is broken down into pure QED,electroweak, and hadronic contributions. The pure QED contribution is by far the largest and has been evaluatedup to and including O(alpha5) with negligible numerical uncertainty. The electroweak contribution is suppressed by(mmu=MW)2 and only shows up at the level of the seventh significant digit. It has been evaluated up to two loops andis known to better than one percent. Hadronic contributions are the most diffcult to calculate and are responsible foralmost all of the theoretical uncertainty. The leading hadronic contribution appears at O(alpha2) and is due to hadronicvacuum polarization, whereas at O(alpha3) the hadronic light-by-light scattering contribution appears. Given the lowcharacteristic scale of this observable, these contributions have to be calculated with nonperturbative methods, inparticular, dispersion relations and the lattice approach to QCD. The largest part of this review is dedicated to adetailed account of recent efforts to improve the calculation of these two contributions with either a data-driven,dispersive approach, or a first-principle, lattice-QCD approach. The final result reads aSMmu = 116 591 810(43) cdot 10^-11and is smaller than the Brookhaven measurement by 3.7sigma. The experimental uncertainty will soon be reduced by upto a factor four by the new experiment currently running at Fermilab, and also by the future J-PARC experiment. Thisand the prospects to further reduce the theoretical uncertainty in the near future—which are also discussed here—makethis quantity one of the most promising places to look for evidence of new physics.