A fresh look at hadronic light-by-light scattering in the muon g-2 with the Dyson-Schwinger approach

TL;DR

This paper uses Dyson-Schwinger equations to calculate the hadronic light-by-light scattering contribution to the muon g-2, providing new estimates that refine the theoretical prediction and reduce the discrepancy with experimental measurements.

Contribution

It introduces a Dyson-Schwinger approach to compute hadronic light-by-light scattering in muon g-2, highlighting the impact of dressing effects on the quark loop contribution.

Findings

Quark loop contribution is larger than previous estimates.

Meson exchange contribution aligns with prior calculations.

Total muon g-2 estimate reduces the theory-experiment discrepancy to 1.9 sigma.

Abstract

We present first results for the hadronic light-by-light scattering contribution to the anomalous magnetic moment of the muon a_{\mu} in the framework of Dyson-Schwinger and Bethe-Salpeter equations. We determine the quark loop and pseudoscalar ({\pi}^0, {\eta}, {\eta}') meson exchange diagram using a phenomenological model for the combined strength of the gluon propagator and the quark-gluon interaction as the only input. Our result for meson exchange, a_{\mu}^{LBL;PS}=(84 \pm 13) x 10^{-11}, is commensurate with previous calculations. However, our number for the quark loop contribution, a_{\mu}^{LBL;quarkloop} = (107 \pm 2 \pm 46) x 10^{-11}, is significantly larger due to dressing effects in the quark propagator and the quark-photon vertex. Taken at face value, this then leads to a revised estimate of the total a_{\mu}=116 591 865.0(96.6) x 10^{-11}, which reduces the difference between theory and experiment to about 1.9 {\sigma}.