[Paper Review] The phase structure of lattice QCD with Wilson quarks and renormalization group improved gluons

F. Farchioni, K. Jansen+7 more|arXiv (Cornell University)|Oct 21, 2004

Quantum Chromodynamics and Particle Interactions22 citations

TL;DR

This study investigates the phase structure of lattice QCD using Wilson fermions with the DBW2 gauge action instead of the standard Wilson plaquette action. It finds that the DBW2 action reduces the minimal pion mass and the jump in the average plaquette, indicating a milder first-order phase transition, while also lowering computational costs compared to the Wilson plaquette action at similar lattice spacings.

ABSTRACT

The effect of changing the lattice action for the gluon field on the recently observed [1] first order phase transition near zero quark mass is investigated by replacing the Wilson plaquette action by the DBW2 action. The lattice action for quarks is unchanged: it is in both cases the original Wilson action. It turns out that Wilson fermions with the DBW2 gauge action have a phase structure where the minimal pion mass and the jump of the average plaquette are decreased, when compared to Wilson fermions with Wilson plaquette action at similar values of the lattice spacing. Taking the DBW2 gauge action is advantageous also from the point of view of the computational costs of numerical simulations.

Motivation & Objective

• To examine how replacing the Wilson plaquette gauge action with the DBW2 action affects the phase structure of lattice QCD with Wilson fermions.
• To assess whether the DBW2 action mitigates the first-order phase transition observed near zero quark mass in previous studies.
• To evaluate the computational efficiency of simulations using the DBW2 gauge action compared to the standard Wilson plaquette action.
• To determine if the DBW2 action leads to a more favorable parameter space for studying chiral symmetry breaking and the QCD phase transition.

Proposed method

• The lattice action for quarks is fixed as the original Wilson fermion action in both cases.
• The gauge action is switched from the standard Wilson plaquette to the renormalization group improved DBW2 action.
• Simulations are performed at similar lattice spacings to compare phase transition characteristics.
• Key observables such as the average plaquette and the pion mass are monitored to detect changes in the phase structure.
• The behavior of the minimal pion mass and the discontinuity in the plaquette are used as indicators of the phase transition strength.

Experimental results

Research questions

• RQ1 How does the choice of gauge action (DBW2 vs. Wilson plaquette) affect the phase structure of lattice QCD with Wilson fermions?
• RQ2 Does the DBW2 gauge action reduce the severity of the first-order phase transition near zero quark mass?
• RQ3 What is the impact of the DBW2 action on the minimal pion mass in the chiral limit?
• RQ4 How does the DBW2 action compare to the Wilson plaquette action in terms of computational cost for numerical simulations?

Key findings

• The DBW2 gauge action reduces the minimal pion mass compared to the Wilson plaquette action at similar lattice spacings.
• The jump in the average plaquette is significantly decreased when using the DBW2 action, indicating a milder first-order phase transition.
• The phase transition region is shifted, suggesting improved control over the chiral limit with the DBW2 action.
• The DBW2 action leads to lower computational costs in numerical simulations compared to the Wilson plaquette action.