Quasinormal modes and holography

TL;DR

The paper establishes a general holographic framework linking quasinormal modes of AdS black branes to the poles of real-time thermal correlators in the dual field theory. By employing gauge-invariant bulk variables and appropriate horizon-boundary conditions, it shows that quasinormal spectra precisely reproduce the pole structure of R-current and stress-energy tensor correlators in strongly coupled N=4 SYM at large Nc. In the AdS5 context, the authors compute the full quasinormal spectra in the vector and tensor sectors, recovering hydrodynamic diffusion for R-charges, shear viscosity–related diffusion, and sound modes with the correct speeds and attenuation constants, while scalar channels exhibit discrete non-hydrodynamic poles. The results illuminate the real-time dynamics of strongly coupled plasmas and illustrate a robust, gauge-invariant method for extracting spectral data from holography, with implications for the interpretation of quasi-particles and transport properties at large N_c.

Abstract

Quasinormal frequencies of electromagnetic and gravitational perturbations in asymptotically AdS spacetime can be identified with poles of the corresponding real-time Green's functions in a holographically dual finite temperature field theory. The quasinormal modes are defined for gauge-invariant quantities which obey incoming-wave boundary condition at the horizon and Dirichlet condition at the boundary. As an application, we explicitly find poles of retarded correlation functions of R-symmetry currents and the energy-momentum tensor in strongly coupled finite temperature N=4 supersymmetric SU(Nc) Yang-Mills theory in the limit of large Nc.