Surface tension in finite-temperature quantum chromodynamics

In a first-order phase transition two phases can coexist at the critical point. The surface free energy α, associated with the interface separating the two phases, is an important parameter for the phenomenology of nucleation in supercooled matter and, more generally, for the whole dynamics of a system undergoing the phase transition. We report on a calculation of the surface tension in quenched QCD on lattices with volumes 6²×{}12×{}2, 8²×{}16×{}2, and 10²×{}20×{}2, as well as on 8²×{}16×{}4 and 12²×{}24×{}4. Our results have been obtained from a Monte Carlo simulation where one half of the lattice is adiabatically brought from one phase to the other by applying a temperature gradient, and where the variation of free energy is calculated at the same time through the average of the action. For Nₜ=2 lattices, we find αTc³=0.23(3) and 0.28(9) on 8²×{}16 and 10²×{}20 spatial volumes, respectively. On the other hand, the results from lattices with Nₜ=4 are less well defined and are compatible with a vanishing surface tension. We discuss possible ways to improve the accuracy of the calculation with larger Nₜ. In particular we propose the use of the Wilson action supplemented with external Polyakov fields as a way to enhance the formation of the interface.