Speaker
Description
In this talk I will discuss the recently introduced frequency-splitting estimators
of quark-line disconnected diagrams in lattice QCD. The evaluation of these diagrams is
required for many phenomenologically interesting observables, but suffers from large statistical
errors due to the vacuum and the random-noise contributions to their variances. Multi-level integration
has the potential to improve dramatically the precision of the computation of these observables once
the random noise due to auxiliary stochastic fields is kept below the intrinsic gauge noise.
After reviewing the theoretical analysis of the variances, I will introduce a new family of stochastic
estimators of single-propagator traces built upon a frequency splitting combined with a hopping expansion of
the quark propagator, and test their efficiency in two-flavour QCD with pions as light as 190 MeV.
The use of these estimators reduces the cost of computing single-trace propagators by one to two orders of magnitude over standard estimators depending on the fermion bilinear.
As a concrete application, I will show the impact of these findings on the computation of
the hadronic vacuum polarization contribution to the muon anomalous magnetic moment.