Evaluation of the Free Energy of Two-Dimensional Yang-Mills Theory
  The free energy in the weak-coupling phase of two-dimensional Yang-Mills theory on a sphere for SO(N) and Sp(N) is evaluated in the 1/N expansion using the techniques of Gross and Matytsin. Many features of Yang-Mills theory are universal among different gauge groups in the large N limit, but significant differences arise in subleading order in 1/N. 
M. Crescimanno, S. G. Naculich, and H. J. Schnitzer