A finite box as a tool to distinguish free quarks from confinement at high temperatures

TL;DR

The paper proposes a novel finite-box method to distinguish free quarks from confined quarks in QCD at high temperatures, supported by lattice calculations showing a diffractive pattern only in the free quark scenario.

Contribution

It introduces a new finite-volume technique to identify quark confinement, validated by lattice QCD simulations demonstrating the presence or absence of a diffractive pattern.

Findings

Diffractive pattern appears for free quarks in finite volume.

No diffractive pattern observed in full QCD, indicating confinement.

Pattern vanishes in infinite volume and continuum limits.

Abstract

Above the pseudocritical temperature T_c of chiral symmetry restoration a chiral spin symmetry (a symmetry of the color charge and of electric confinement) emerges in QCD. This implies that QCD is in a confining mode and there are no free quarks. At the same time correlators of operators constrained by a conserved current behave as if quarks were free. This explains observed fluctuations of conserved charges and the absence of the rho-like structures seen via dileptons. An independent evidence that one is in a confining mode is very welcome. Here we suggest a new tool how to distinguish free quarks from a confining mode. If we put the system into a finite box, then if the quarks are free one necessarily obtains a remarkable diffractive pattern in the propagator of a conserved current. This pattern is clearly seen in a lattice calculation in a finite box and it vanishes in the infinite volume limit as well as in the continuum. In contrast, the full QCD calculations in a finite box show the absence of the diffractive pattern implying that the quarks are confined.