After the fluid: subexponential decay in AdS4

A bstract We study the late-time behaviour of nonlinear perturbations of Schwarzschild-AdS 4 black branes and show that real-analytic initial data generically enter a regime controlled by the large- k tail of the quasinormal mode spectrum { ω k n }. Using the asymptotic scaling Im ω k n ~ k −1/5 of the planar AdS 4 black brane, we derive a universal prediction that boundary observables decay in a stretched-exponential manner, specifically as exp(− c t 5/6 ) up to a mild polynomial prefactor. Fully nonlinear numerical evolutions employing Fourier spectral and discontinuous Galerkin methods confirm this behaviour for small black holes and show consistent scaling — after suppressing long-lived low- k modes — for larger ones. These results indicate that stretched-exponential decay with exponent 5 / 6 is a robust feature of AdS 4 gravitational dynamics with real-analytic data, arising from geometric-optics physics rather than hydrodynamic modes.