Epsilon regime calculations with reweighted clover fermions

TL;DR

This paper introduces a reweighting method for dynamical lattice QCD simulations at small quark masses, successfully reaching the epsilon regime and enabling the extraction of low energy constants with controlled fluctuations.

Contribution

It demonstrates the effectiveness of stochastic reweighting in dynamical simulations to access the epsilon regime, avoiding technical difficulties of direct simulations.

Findings

Reweighting factors fluctuate moderately on nHYP smeared ensembles.

Large overlap between original and reweighted configurations for various observables.

Successful reweighting from higher to lower quark masses in different volumes.

Abstract

We perform fully dynamical simulations at small quark masses by reweighting in the quark mass, calculating the weight factors stochastically. This approach avoids some of the technical difficulties associated with direct simulations. We find that the weight factors fluctuate only moderately on nHYP smeared dynamical Wilson-clover ensembles, and demonstrate that the overlap between the original and reweighted configurations is large both for short and long distance observables. We could successfully reweight 16^4, (1.85fm)^4 volume configurations from m_q 20 MeV to m_q~5 MeV, and 24^4, (2.77fm)^4 configurations from m_q~8MeV to m_q~MeV quark masses, reaching the epsilon-regime. Using the pseudoscalar and axialvector correlators we predict the low energy constants Sigma and F and study their volume and mass dependence.