Thermodynamics of SU(N) Yang-Mills theories in 2+1 dimensions I - The confining phase

We compute the equation of state in the confining phase of SU(N) Yang-Mills theories with N=2, 3, 4, 5 and 6 colors in 2+1 dimensions, via lattice simulations. At low enough temperatures, the results are accurately described by a gas of glueballs, including all known states below the two-particle threshold. Close to the deconfinement temperature, however, this prediction underestimates the numerical results, and the contribution from heavier glueballs has to be included. We show that the spectral density of the latter can be accurately described using a simple bosonic string model.
Comment: 1+22 pages, 8 eps figures; v2: added comments about the uncertainties on the temperature scale and the pressure, expanded the discussion in section 4, added references: version published in JHEP