Low temperature dominance of pionlike excitations in the massive Gross-Neveu model at order 1/N

We perform a 1/N expansion of the partition function of the massive Gross-Neveu model in 1+1 dimensions. The procedure allows for the inclusion of the contribution of scalar and pseudoscalar composites (of order 1/N) to the equation of state. The naive expectation that the bosonic fluctuations significantly correct the mean field approximation at low temperatures is confirmed by our calculations. Actually the relevant degrees of freedom of hadronic matter at low temperatures are found to be pionlike excitations, rather than the fundamental constituents.