Finite Temperature Tunneling and Phase Transitions in SU(2)-Gauge Theory
  A pure Yang-Mills theory extended by addition of a quartic term is considered in order to study the transition from the quantum tunneling regime to that of classical, i.e. thermal, behaviour. The periodic field configurations are found, which interpolate between the vacuum and sphaleron field configurations. It is shown by explicit calculation that only smooth second order transitions occur for all permissible values of the parameter $\L$ introduced with the quartic term. The theory is one of the rare cases which can be handled analytically. 
A. V. Shurgaia, H. J. W. Mueller-Kirsten, J.-Q. Liang and D. K. Park