CRITICAL-BEHAVIOR OF HETEROTIC STRINGS TO ALL ORDERS IN STRING PERTURBATION-THEORY

Using an explicit expression for the thermal soliton sector, we compute the would-be divergent terms of the free energy of heterotic strings when a nontrivial homology cycle in the Riemann surface is pinched. Modulo a plausible hypothesis, we find exactly the same critical temperature as in the lowest order. We also make some comments on the validity of our hypothesis. Our result is consistent with recent findings on the constant asymptotic form of the decay width for closed strings.