The Hagedorn transition and the number of degrees of freedom of string theory

Extending recent discussions of the Hagedorn transition in string theory, we argue that this transition is a first-order phase transition with a very large heat (corresponding to a genus-zero contribution to the free energy that appears above the critical temperature). Formally analyzing the k-loop contributions to the free energy at temperatures far above the Hagedorn temperature leads to a number of interesting speculations about the underlying degrees of freedom in string theory.