SU(2) lattice gauge theory in 2+1 dimensions: Critical couplings from twisted boundary conditions and universality

We present a precision determination of the critical coupling βc for the deconfinement transition in pure SU(2) gauge theory in 2+1 dimensions. This is possible from universality, by intersecting the center vortex free energy as a function of the lattice coupling β with the exactly known value of the interface free energy in the 2D Ising model at criticality. The method allows us to find critical couplings with unprecedented numerical accuracy. Results for lattices with different numbers of sites Nt along the Euclidean time direction are used to determine how β varies with temperature for a given Nt around the deconfinement transition.