Speaker
Description
As the only lattice vector current that does not require renormalisation is the point-split conserved current it is convenient to have a robust, precise and computationally cheap methodology for the calculation of vector current renormalisation factors, $Z_V$. Momentum subtraction schemes, such as RI-SMOM, implemented nonperturbatively on the lattice provide such a method if it can be shown that the systematic errors, e.g. from condensates, are well controlled.
We present $Z_V$ calculations in a variety of momentum subtraction schemes and for a variety of currents including the conserved current, using the HISQ action. We compare the results with each other, with previous HISQ determinations using form factors at $q^2=0$ and with perturbation theory. Our results show that momentum subtraction schemes, suitably defined, allow for good control of $Z_V$ determination at small lattice spacings as well as the inclusion of electromagnetic effects. Both of these are potentially important for the Fermilab/HPQCD/MILC programme to calculate the leading order hadronic vacuum polarisation contribution to the anomalous magnetic moment of the muon, among other calculations.
