Absorption Lengths in the Holographic Plasma

TL;DR

This paper studies how periodic perturbations affect the holographic N=4 plasma, calculating absorption lengths and screening lengths via complex wave numbers derived from wave equations in AdS black hole backgrounds, revealing their relation to glueball masses.

Contribution

It introduces a method to compute absorption and screening lengths in holographic plasma using complex wave numbers from quasinormal mode analysis, linking these to physical properties like glueball masses.

Findings

Absorption lengths are obtained from complex wave numbers in AdS black hole backgrounds.

Screening length at zero frequency relates to static field and glueball masses.

Longest screening length is associated with an operator carrying R-charge.

Abstract

We consider the effect of a periodic perturbation with frequency $\omega$ on the holographic N=4 plasma represented by the planar AdS black hole. The response of the system is given by exponentially decaying waves. The corresponding complex wave numbers can be found by solving wave equations in the AdS black hole background with infalling boundary conditions on the horizon in an analogous way as in the calculation of quasinormal modes. The complex momentum eigenvalues have an interpretation as poles of the retarded Green's functions, where the inverse of the imaginary part gives an absorption length $\lambda$. At zero frequency we obtain the screening length for a static field. These are directly related to the glueball masses in the dimensionally reduced theory. We also point out that the longest screening length corresponds to an operator with non-vanishing R-charge and thus does not have an interpretation as a QCD3 glueball.