Simulations of Lattice Fermions with Chiral Symmetry in Quantum Chromodynamics

TL;DR

This thesis investigates numerical simulations of lattice fermions with chiral symmetry in QCD, comparing different formulations, validating against theoretical predictions, and estimating physical constants like the pion decay constant.

Contribution

It introduces a comparison of Neuberger and hypercube overlap operators in the epsilon-regime and explores a topology conserving gauge action for efficient sampling.

Findings

Good agreement with chiral random matrix theory for volumes larger than 1.12 fm

Estimated the pion decay constant F_pi from eigenvalue distributions

Identified a promising gauge action for epsilon-regime simulations

Abstract

This thesis is dedicated to explore the feasibility of numerical calculations in the $\epsilon$--regime of QCD for the extraction of physical information. We apply two formulations of the Ginsparg-Wilson fermions the Neuberger operator and the hypercube overlap operator to compute the observables of interest. As a main result we present the comparison of the distributions of the leading individual eigenvalues of the Neuberger operator in QCD and the analytical predictions of chiral random matrix theory. We observe a good agreement as long as each side of the physical volume exceeds about $L\approx 1.12\fm$. It turns out that this bound for $L$ is generic and sets the size of the physical volume where the axial correlator behaves according to chiral perturbation theory. This allows us to compute a value for the pion decay constant $F_{\pi}$. As an alternative procedure we only consider the contribution from the zero modes. Here we are able to obtain an estimate for $F_{\pi}$ and $\alpha$. As a theoretical development the L\"uscher topology conserving gauge action is investigated. This enables us to sample the observables of interest in the $\epsilon$--regime without recomputing the index. We can report that a promising gauge action has been identified.