On the nature of the Hagedorn transition in NCOS systems

We extend the study of the nature of the Hagedorn transition in NCOS system s in various dimensions. The canonical analysis results in a microscopic io nization picture of a bound state system in which the Hagedorn transition i s postponed till irrelevancy. A microcanonical analysis leads to a limiting Hagedorn behaviour dominated by highly excited, long open strings. The stu dy of the full phase diagram of the NCOS system using the AdS/CFT correspon dence suggests that the microscopic ionization picture is the correct one. We discuss some refinements of the ionization mechanism for d > 2 NCOS syst ems, including the formation of a temperature-dependent barrier for the pro cess. Some possible consequences of this behaviour, including a potential p uzzle for d = 5, are discussed. Phase diagrams of a regularized form of NCO S systems are introduced and do accomodate a phase of long open strings whi ch disappears in the strict NCOS limit.