Universal critical dynamics in QCD

by Mr Johannes Roth (Giessen University)

Thursday 30 Jan 2025, 14:15 → 15:45 Europe/Berlin

Abbeanum/Ground floor-HS 2 - Hörsaal 2 (TPI, FSU Jena)

In this talk, I will give a general overview on how the complicated real-time dynamics of hot QCD matter close to a second-order phase transition can be understood through universality. There not only the static thermodynamic properties become universal, but also the dynamics. By appealing to universality, this means that one can instead analyze a simpler system from the same "dynamic universality class". I will focus on two particular second-order phase transitions: the chiral phase transition in the chiral limit, and the critical point at finite baryon chemical potential and quark masses. In the former case, I will review the argument by Rajagopal and Wilczek that the associated dynamic universality class belongs to that of an O(4) Heisenberg antiferromagnet (which is called "Model G" in the classification of Halperin and Hohenberg). Based on a novel real-time formulation of the functional renormalization group I will present results for dynamic universal quantities, including the non-trivial value z=d/2 of the dynamic critical exponent (where d is the number of spatial dimensions) and dynamic universal scaling functions. Moving away from the chiral limit, I will show how the same method can also be used to study the universal dynamics around the conjectured QCD critical point at finite baryon chemical potential and quark masses. I will review the argument by Son and Stephanov that the associated dynamic universality class belongs to that of a liquid-gas transition in a pure fluid (called "Model H"), and show results for dynamic critical exponents. Finally, I will outline commonalities and differences of Models G and H such as weak-scaling relations which hold in either case versus the characteristic strong scaling of Model G which is absent in Model H.