Efficient simulations with electrically-charged sea-quarks at O($\alpha$)

by Dr Tim Harris (ETH Zürich)

Monday 28 Nov 2022, 13:00 → 14:00 Europe/Berlin

2.049 (IRIS)

Lattice QCD computations of hadronic matrix elements required for precision tests of the Standard Model are now targetting an accuracy where the electromagnetic interactions of the quarks can no longer be neglected. Expanding in the electromagnetic coupling $\alpha$ introduces many quark-line disconnected diagrams, associated with the contribution of electrically-charged sea quarks to the observable of interest, which cannot be omitted a priori. In this talk, I aim to outline why these diagrams are particularly challenging to compute and how they might be efficiently included in lattice simulations of QCD+QED. I begin with an analysis of the quark-line disconnected contribution to the leading-order hadronic vacuum polarization, which can be adapted for some of the contributions to the current correlators which parameterize electromagnetic interactions with the sea quarks. Some simple decompositions may be sufficient to compute the remaining diagrams with enough precision so that they can be incorporated in future lattice computations, meaning that all sources of isospin-breaking effects can be controlled. 

harris_berlin_2022_vonline.pdf