Universal Pseudo-Goldstone Damping from the Real-Time Functional Renormalization Group

Strongly correlated systems, from QCD matter to condensed matter, exhibit universal dynamics near phase transitions. However, despite the successes of various theoretical approaches, systematic treatments of fluctuations are scarce. This talk unveils a novel universal damping mechanism for pseudo-Goldstone modes in systems with spontaneously broken approximate symmetries. I will introduce the real-time functional renormalization group (fRG) method, a powerful non-perturbative framework for studying real-time dynamics near critical points. Using this approach within a critical O(N) model, we uncover a new universal scaling for pseudo-Goldstone damping. Different from the conventional damping found in holography and hydrodynamics, the new one is controlled by critical fluctuations, hence is invisible in mean-field systems or strongly correlated systems with classical gravity duals. Since the critical damping depends solely on the universalities of the critical point, irrespective of the microscopic details, our conclusion should be applicable to a wide class of interacting systems.