Self-interacting QCD strings and string balls

Abstract

Strings at $T\ensuremath{\approx}{T}_{c}$ are known to be subject to the so-called Hagedorn phenomenon, in which a string's entropy (times $T$) and energy cancel each other and result in the evolution of the string into highly excited states, or ``string balls.'' Intrinsic attractive interaction of strings---gravitational for fundamental strings or in the context of holographic models of the AdS/QCD type, or $\ensuremath{\sigma}$ exchanges for QCD strings---can significantly modify properties of the string balls. If heavy enough, those start approaching properties of the black holes. We generate self-interacting string balls numerically, in a thermal string lattice model. We found that in a certain range of the interaction coupling constants they morph into a new phase, the ``entropy-rich'' string balls. These objects can appear in the so-called mixed phase of hadronic matter, produced in heavy ion collisions, as well as possibly in the high multiplicity proton-proton or proton-nucleus collisions. Among discussed applications are jet quenching in the mixed phase and also the study of angular deformations of the string balls.