Quasi-normal modes of a strongly coupled non-conformal plasma and approach to criticality

TL;DR

This paper investigates the behavior of strongly coupled non-conformal plasmas near criticality using holographic methods, revealing the quasi-normal mode spectrum and its transition to a branch cut at the critical point.

Contribution

It provides an analytical calculation of quasi-normal modes in a non-conformal plasma approaching criticality, connecting IR and UV geometries and describing mode accumulation.

Findings

Quasi-normal modes form a branch cut at criticality.

Near criticality, two sets of modes emerge from IR and UV geometries.

The spectrum is analytically obtained in a specific limit.

Abstract

We study fluctuations around equilibrium in a class of strongly interacting non-conformal plasmas using holographic techniques. In particular we calculate the quasi-normal mode spectrum of black hole backgrounds that approach to Chamblin-Reall plasmas in the IR. In a specific limit, related to the exact linear-dilaton background in string theory, we observe that the plasma approaches criticality and we obtain the quasi-normal spectrum analytically. We regulate the critical limit by gluing the IR geometry that corresponds to the non-conformal plasma to a part of AdS space-time in the UV. Near criticality, we find two sets of quasi-normal modes, related to the IR and UV parts of the geometry. In the critical limit, the quasi-normal modes accumulate to form a branch cut in the correlators of the energy-momentum tensor on the real axis of the complex frequency plane.