The strong interaction, emergent phenomena and heavy-ion collisions

Abstract: Among the four fundamental actions in nature, the strong interaction is arguably the most mysterious. Foremost, the strongly interacting particles seen in nature, hadrons like protons and neutrons, are not themselves the basic degrees of freedom of the underlying theory, Quantum Chromo Dynamics (QCD). Rather, the hadrons emerge as complex structures from interactions of the basic building blocks of QCD, quarks and gluons. Calculations suggested that at high temperature and density hadrons should melt into a new state of matter, the Quark-Gluon Plasma. Surprisingly, this state also exhibits novel collective phenomena, which can be studied in nuclear collisions at high energy. I will discuss current results and point out how future experiments can help us understand emergent QCD phenomena in different energy regimes.