Transport peak in thermal spectral function of ${\cal N}=4$
supersymmetric Yang-Mills plasma at intermediate coupling
Physical Review Letters American Physical Society (2018)
Authors:
Jorge Casalderrey-Solana, Sašo Grozdanov, Andrei O Starinets
Abstract:
We study the structure of thermal spectral function of the stress-energy
tensor in ${\cal N}=4$ supersymmetric Yang-Mills theory at intermediate 't
Hooft coupling and infinite number of colors. In gauge-string duality, this
analysis reduces to the study of classical bulk supergravity with
higher-derivative corrections, which correspond to (inverse) coupling
corrections on the gauge theory side. We extrapolate the analysis of
perturbative leading-order corrections to intermediate coupling by
non-perturbatively solving the equations of motion of metric fluctuations dual
to the stress-energy tensor at zero spatial momentum. We observe the emergence
of a separation of scales in the analytic structure of the thermal correlator
associated with two types of characteristic relaxation modes. As a consequence
of this separation, the associated spectral function exhibits a narrow
structure in the small frequency region which controls the dynamics of
transport in the theory and may be described as a transport peak typically
found in perturbative, weakly interacting thermal field theories. We compare
our results with generic expectations drawn from perturbation theory, where
such a structure emerges as a consequence of the existence of quasiparticles.
