Dimensionally regularized Polyakov loop correlators in hot QCD

TL;DR

This paper computes the singlet quark-antiquark free energy in hot QCD at order O(alpha_s^2), analyzing its behavior across distance scales, and compares the results with lattice data to improve understanding of finite-temperature QCD observables.

Contribution

It provides a continuum, perturbative calculation of the singlet free energy at order O(alpha_s^2), including new results for pure SU(Nc) and full QCD, and discusses gauge dependence and lattice comparisons.

Findings

At short distances, matches zero-temperature potential behavior.

At large distances, exhibits a gauge-dependent power-law tail.

Recomputes the infinite-distance limit, finding a different non-logarithmic term for SU(Nc).

Abstract

A popular observable in finite-temperature lattice QCD is the so-called singlet quark-antiquark free energy, conventionally defined in Coulomb gauge. In an effort to interpret the existing numerical data on this observable, we compute it at order O(alpha_s^2) in continuum, and analyze the result at various distance scales. At short distances (r << 1/pi T) the behaviour matches that of the gauge-independent zero-temperature potential; on the other hand at large distances (r >> 1/pi T) the singlet free energy appears to have a gauge-fixing related power-law tail. At infinite distance the result again becomes physical in the sense that it goes over to a gauge-independent disconnected contribution, the square of the expectation value of the trace of the Polyakov loop; we recompute this quantity at O(alpha_s^2), finding for pure SU(Nc) a different non-logarithmic term than in previous literature, and adding for full QCD the quark contribution. We also discuss the value of the singlet free energy in a general covariant gauge, as well as the behaviour of the cyclic Wilson loop that is obtained if the singlet free energy is made gauge-independent by inserting straight spacelike Wilson lines into the observable. Comparisons with lattice data are carried out where possible.