[NT/RBRC seminar] Stable and unstable perturbations in universal scaling phenomena far from equilibrium

by Thimo Preis (Heidelberg University)

Friday 12 May 2023, 11:00 → 17:00 US/Eastern

Large seminar room (https://bnl.zoomgov.com/j/1614715193?pwd=WkwxODVWdzZzb29zQnZRVGp3VTBDQT09)

Universal self-similar scaling associated to non-thermal attractors arises in a wide variety of systems across different energy scales, from turbulent thermalization in the Glasma to far-from-equilibrium Bose condensation in ultracold atomic gases. It is a great challenge to understand the emergent stability properties in such self-organized scaling phenomena from the underlying quantum dynamics. For an N-component scalar quantum field theory, I will present a study of the dynamics of perturbations around nonthermal fixed points associated to universal scaling phenomena in quantum many-body systems far from equilibrium. While the approach to universal scaling behavior of this system is known to be observed from a wide range of far-from-equilibrium initial conditions without fine-tuning, we find both stable and unstable perturbations around the scaling solution to be present. With the help of linear response theory, I will discuss how unstable dynamics arises from a competition between elastic scattering processes among the  quasi-particle states. We find that the fixed point is rendered dynamically attractive at any non-zero momentum due to universal scaling of the unstable regime towards the infrared by virtue of a self-similar quasi-particle cascade.