Scaling, topological tunneling and actions for weak coupling DWF calculations

TL;DR

This paper investigates strategies to improve topological tunneling in lattice QCD with domain wall fermions at weak coupling, focusing on autocorrelation times and boundary conditions to facilitate simulations relevant for charm physics.

Contribution

It evaluates the effectiveness of open boundary conditions and a dislocation-enhancing determinant in reducing autocorrelation times for topological charge in weak coupling DWF calculations.

Findings

Open boundary conditions do not prevent long autocorrelation times.

Dislocation-enhancing determinant can increase topological tunneling.

Results are relevant for simulations targeting charm physics.

Abstract

We present results from a 2+1 flavor DWF calculation at 1/a = 3 GeV and discuss strategies for similar calculations at finer lattice spacings which will target charm physics. At weak coupling the autocorrelation time of the global topological charge becomes very long because the HMC algorithm has trouble moving between topological sectors. We report the results of simulations that test two ideas for reducing the autocorrelation time of topological charge. In weak coupling quenched simulations we find that the open boundary conditions suggested by L\"uscher and Schaefer do not prevent the appearance of extremely long autocorrelation times for topological observables. We discuss the idea of a "dislocation-enhancing determinant" and show that it can produce an increase in topological tunneling.