Self-interacting QCD strings and string balls
  Strings at T ~ 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 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. 
Tigran Kalaydzhyan and Edward Shuryak
hep-ph hep-lat hep-th nucl-th