On the supergravity description of boost invariant conformal plasma at strong coupling

TL;DR

This paper investigates the supergravity duals of expanding boost invariant conformal plasmas at strong coupling, revealing limitations of the supergravity approximation and providing insights into plasma relaxation times.

Contribution

It constructs the asymptotic supergravity background for expanding plasmas and analyzes the singularities to determine plasma properties and the validity of the supergravity approximation.

Findings

Absence of curvature singularities determines the plasma's equation of state.

Shear viscosity is fixed by the early-time expansion analysis.

Supergravity approximation fails to fully describe the relaxation time due to unresolved singularities.

Abstract

We study string theory duals of the expanding boost invariant conformal gauge theory plasmas at strong coupling. The dual supergravity background is constructed as an asymptotic late-time expansion, corresponding to equilibration of the gauge theory plasma. The absence of curvature singularities in the first few orders of the late-time expansion of the dual gravitational background unambiguously determines the equilibrium equation of the state, and the shear viscosity of the gauge theory plasma. While the absence of the leading pole singularities in the gravitational curvature invariants at the third order in late-time expansion determines the relaxation time of the plasma, the subleading logarithmic singularity can not be canceled within a supergravity approximation. Thus, a supergravity approximation to a dual description of the strongly coupled boost invariant expanding plasma is inconsistent. Nevertheless we find that the relaxation time determined from cancellation of pole singularities is quite robust.