Complexity in high-energy physics

In addition to its importance in describing high-energy processes themselves, the dynamics of multiparticle production has become part of the general field of non-linear phenomena and complex systems. Multiparticle dynamics is one of the rare fields of physics where higher-order correlations are directly accessible in their full multi-dimensional characteristics under well-controlled experimental conditions. Multi-particle dynamics, therefore, is an ideal testing ground for the development of advanced statistical methods. Higher- order correlations have, indeed, been observed as particle-density fluctuations. Approximate scaling with improving resolution provides evidence for a self-similar correlation effect. Quantum- Chromodynamics branching is a good candidate for a dynamical explanation of these correlations in e **+e**- collisions at CERN/LEP and, as expected, also of those in pp collisions at future CERN/LHC energies. However, also other sources such as identical-particle Bose-Einstein interference effects contribute.