Taste symmetry and QCD thermodynamics with improved staggered fermions

TL;DR

This paper investigates how improved staggered fermion actions, especially HISQ/tree, reduce taste symmetry violations in lattice QCD thermodynamics, leading to more accurate results and better understanding of the QCD phase transition.

Contribution

It provides a systematic comparison of HISQ/tree with other actions, demonstrating significant reduction in taste violations and their impact on thermodynamic quantities in 2+1 flavor QCD.

Findings

HISQ/tree substantially reduces taste violations compared to other actions.

Quantified cut-off effects on thermodynamic observables.

Implications for the QCD equation of state and comparison with hadron resonance gas model.

Abstract

Taste symmetry violations in staggered fermion formulations correlate strongly with the cut-off (lattice spacing) dependence in thermodynamic quantities. Better taste symmetry on the lattice can be achieved either by decreasing the lattice spacing and going to larger temporal extent in finite-temperature calculations, or by further improving the action. The highly improved staggered quark (HISQ) action offers a further degree of improvement and substantially reduces taste violations. We report on our studies of the 2+1 flavor QCD thermodynamics with the HISQ/tree action. By systematically comparing HISQ/tree, asqtad, p4 and stout calculations we quantify how the cut-off effects manifest themselves in different thermodynamic quantities, including the renormalized Polyakov loop, chiral condensate, various fluctuations and correlations of conserved charges. The implications for the equation of state and a comparison to the hadron resonance gas model are also discussed. The chiral aspects of the finite-temperature transition are discussed in the companion HotQCD contribution [1].