Center vortex evidence for a second finite-temperature QCD transition

Abstract

Evidence for the existence of a second finite-temperature transition in quantum chromodynamics (QCD) is obtained through the study of center vortex geometry and its evolution with temperature. The dynamical anisotropic ensembles of the Fastsum Collaboration are utilized to conduct a comprehensive analysis at eight temperatures beyond the established chiral transition. Visualizations of the center vortex structure in temporal and spatial slices of the lattice reveal that vortex percolation persists through the chiral transition and ceases at a temperature that is approximately twice the chiral transition temperature Tc. This implies that confinement is retained through temperatures up to T≈2Tc, pointing toward a second transition corresponding to deconfinement. The loss of percolation is quantified by the vortex cluster extent, providing a clear signal for the deconfinement transition. Additional vortex statistics, including temporal correlations, vortex and branching point densities, the number of secondary clusters and vortex chain lengths between branching points, are scrutinized as a function of temperature. All ten measures investigated herein show the characteristics of two transitions in QCD, encompassing the chiral transition at Tc and the deconfinement transition at T≈2Tc. Performing an inflection point analysis on the vortex and branching point densities produces an estimate of Tc that agrees with the known Fastsum value. By the same procedure, a precise estimate of the deconfinement point is extracted as Td=321(6) MeV. Published by the American Physical Society 2025