Centre vortices in thermal lattice QCD with dynamical fermions

Abstract: Evidence for a second finite-temperature transition in Quantum Chromodynamics (QCD) is revealed through the study of centre vortex geometry and its temperature-dependent evolution. Using the anisotropic dynamical ensembles from the Fastsum collaboration, we conduct a detailed analysis at several temperatures above and below the established chiral transition. Visualisations of the centre vortex structure in temporal and spatial lattice slices demonstrate that vortex percolation persists through the chiral transition and ceases at approximately twice the chiral transition temperature, T_c. This indicates that confinement is maintained up to T \approx 2T_c, suggesting a second transition associated with deconfinement. The loss of percolation, quantified by vortex cluster extent, provides a clear signal for this transition. Statistical analysis of vortex density and cluster extent is presented which reveals consistent evidence of two transitions in QCD: the chiral transition at T_c and the deconfinement transition at T_d \approx 2T_c. By analysing these, and other quantities, we obtain a precise determination of the deconfinement temperature, T_d = 321(6) MeV.