High-temperature strings

The microcanonical density of states for a weakly interacting gas of strings compactified on a torus is computed in the limit of large energy, taking into account conservation of winding number and momentum. These constraints affect the high-energy form of the density of states. Using these results we discuss physical properties of the string ensemble near the Hagedorn temperature. In the free theory the Hagedorn temperature is interpreted as signaling the transition to long string dominance; in the interacting theory the system gravitationally collapses, possibly to a new phase. Formation of long strings may also be relevant to Hawking radiation and to acceleration radiation. (orig.)