What is the Quark-Gluon Plasma made of?

The current paradigm considers the quark-gluon plasma (QGP) as a strongly coupled liquid-like state composed of short-lived quasiparticles. This preprint evaluates the existing paradigm using both perturbative and non-perturbative methods including hard-thermal loop perturbation theory, lattice QCD, and the functional renormalization group.

This preprint surveys the current understanding of the QGP's composition, focusing on the "fully developed" QGP at temperatures beyond the phase transition. While acknowledging the paradigm of a strongly coupled liquid-like QGP, the preprint examines this understanding through various theoretical lenses, primarily thermal perturbation theory. It delves into the quasiparticle structure of the QGP and how this structure changes with interaction strength. The preprint discusses the limitations of perturbative methods and introduces non-perturbative approaches like Lattice QCD and the Functional Renormalization Group to refine the current understanding. The use of multiple theoretical tools combined with experimental observations indicates a drift within the existing model, refining and potentially shifting our understanding of QGP composition but not enough to warrant a Model Crisis. Therefore, it is most appropriately classified as Model Drift. I am uncertain about the exact classification and oscillate between Model Drift and Normal Science because the paper mainly reviews the current paradigm and does not explicitly propose a new model. However, the detailed analysis and identification of existing model limitations suggest that the field is moving towards a more nuanced understanding, drifting away from the purely strongly-coupled liquid picture, hence the primary classification as Model Drift.