Theta sectors and thermodynamics of a classical adjoint gas

The effect of topology on the thermodynamics of a gas of adjoint representation charges interacting via 1 + 1-dimensional SU(N) gauge fields is investigated, We demonstrate explicitly the existence of multiple vacua parameterized by the discrete superselection variable k = 1,..., N. In the low pressure limit, the k dependence of the adjoint gas equation of state is calculated and shown to be non-trivial. Conversely, in the limit of high system pressure, screening by the adjoint charges results in an equation of state independent of k. Additionally, the relation of this model to adjoint QCD at finite temperature in two dimensions and the limit N --> infinity are discussed. (C) 1998 Elsevier Science B.V.