Special seminar: Full QCD+QED simulations versus the RM123 method: a comparison for the U-spin window contribution to $a^{HVP}_\mu$

Title: Full QCD+QED simulations versus the RM123 method: a comparison for the U-spin window contribution to $a^{HVP}_\mu$

Abstract: Achieving sub-percent precision in lattice computations of hadronic observables requires the inclusion of isospin-breaking (IB) effects arising from electromagnetic interactions and the light-quark mass splitting. A prominent example is the leading-order hadronic vacuum polarization contribution to the muon $g-2$, $a^{HVP}_\mu$, which must be determined with permille-level precision to match the experimental accuracy. In lattice calculations, IB corrections are commonly included à la RM123, by perturbatively expanding the observables around the isospin-symmetric theory and computing the corrections order by order in the IB parameters. An alternative approach is to simulate the joint QCD+QED probability distribution directly, which requires a consistent finite-volume formulation of QED. In this talk, I will present the first comparison of the two approaches including the sea-quark effects in both frameworks. In our study, we compute the $U$-spin window contribution to $a^{HVP}_\mu$ in QCD+QED with $N_f=1+2+1$ quark flavours and C* boundary conditions using both approaches. We compare the predictions and their uncertainties at fixed lattice spacing and lattice volume, at a pion mass of 400 MeV. Our findings indicate that, for a fixed number of samples, the dynamical QCD+QED simulations can be advantageous from the point of view of the statistical uncertainty.

When: Monday, 1st of June at 13:15 CET

Where: HU Seminar Room 1.021 and Zoom. The link is given below.