Leading isospin breaking effects in the HVP contribution to $a_{\mu }$ and to the running of $\alpha$

Abstract

The anomalous magnetic moment of the muon $a_{\mu }$ and the running of the electromagnetic coupling $\alpha$ play a fundamental role in beyond Standard Model (SM) physics searches. Non-perturbative hadronic contributions to both quantities, which are related to the hadronic vacuum polarization (HVP) function consisting of two electromagnetic currents, are a main source of uncertainty in the SM prediction. We compute the HVP function in lattice QCD+QED applying the time-momentum representation method. We expand the relevant correlation functions around the isosymmetric limit. In particular, we focus on leading isospin breaking effects taking quark-connected contributions into account, which we evaluate on isosymmetric $N_{\mathrm{f}}=2+1$ QCD gauge ensembles generated by the CLS initiative with non-perturbatively $O(a)$-improved Wilson fermions.

Comments: 9 pages, 3 figure, proceedings to talk presented at the 38th International Symposium on Lattice Field Theory, 26th-30th July, Zoom/Gather@Massachusetts Institute of Technology, MA, USA