Quasinormal Modes of Nonthermal Fixed Points

Quasinormal modes play a prominent role in the relaxation of diverse physical systems to equilibria, ranging from astrophysical black holes to tiny droplets of quark-gluon plasma at the RHIC and LHC accelerators. We propose that a novel kind of quasinormal mode governs the direct approach to self-similar time evolution of nonthermal fixed points, whose relevance ranges from high-energy physics to cold atom gases. We utilize black hole perturbation theory techniques to compute the spectrum of these far-from-equilibrium quasinormal modes for a kinetic theory with a Fokker-Planck collision kernel in isotropic and homogeneous states. Our conclusion is that quasinormal modes of nonthermal fixed points give rise to a tower of progressively more decaying power-law contributions. A by-product of our analysis is a precise determination and improved understanding of the distribution function characterizing nonthermal fixed points.