Instability in the Molecular Dynamics Step of Hybrid Monte Carlo in Dynamical Fermion Lattice QCD Simulations

TL;DR

This paper studies the causes of instability and irreversibility in Hybrid Monte Carlo simulations for lattice QCD, identifying parameter regimes for stable, reversible computations and optimizing simulation parameters.

Contribution

It provides a detailed analysis of instability sources in HMC for lattice QCD and establishes parameter limits for stable, reversible simulations with improved Wilson fermions.

Findings

Identified parameter ranges ensuring stability and reversibility.

Compared empirical results with theoretical expectations.

Optimized tolerance parameters for better simulation stability.

Abstract

We investigate instability and reversibility within Hybrid Monte Carlo simulations using a non-perturbatively improved Wilson action. We demonstrate the onset of instability as tolerance parameters and molecular dynamics step sizes are varied. We compare these findings with theoretical expectations and present limits on simulation parameters within which a stable and reversible algorithm is obtained for physically relevant simulations. Results of optimisation experiments with respect to tolerance prarameters are also presented.