Speaker
Description
We propose a hybrid reweighting method to calculate expectation values of observables in the presence of external fields coupled to dynamical fermions. The reweighting factor is calculated from the ratio of fermion determinants with and without the external field, evaluated on a background of Wilson-flowed dynamical gauge fields. Because the Wilson flow greatly reduces ultraviolet fluctuations, this determinant ratio can be efficiently evaluated numerically using the worldline formalism, after applying a Whittaker-Shannon-type interpolation to embed the discrete lattice configurations into continuous space. Under fixed flow times, we can take the lattice continuum limit of the reweighted data along standard continuum trajectories. With the addition of appropriate counterterms and renormalization, physical results are obtained from a smooth extrapolation to the zero-flow-time limit.
As a primary example, we discuss the application of this method to physical systems, particularly QED in non-trivial backgrounds below the Schwinger pair-production threshold.