On the nature of the Hagedorn transition in NCOS systems

ABSTRACT: We extend the study of the nature of the Hagedorn transition in NCOS systems in various dimensions. The canonical analysis results in a microscopic ionization picture of a bound state system in which the Hagedorn transition is postponed till irrelevancy. A microcanonical analysis leads to a limiting Hagedorn behaviour dominated by highly excited, long open strings. The study of the full phase diagram of the NCOS system using the AdS/CFT correspondence suggests that the microscopic ionization picture is the correct one. We discuss some refinements of the ionization mechanism for d > 2 NCOS systems, including the formation of a temperature-dependent barrier for the process. Some possible consequences of this behaviour, including a potential puzzle for d = 5, are discussed. Phase diagrams of a regularized form of NCOS systems are introduced and do accomodate a phase of long open strings which disappears in the strict NCOS limit.