AdS gravastar and its signatures from dual conformal field theory

TL;DR

The paper investigates how horizon-scale quantum gravity effects in an AdS gravastar—an ECO formed by gluing an AdS-Schwarzschild exterior to a de Sitter interior—manifest in the dual CFT via the retarded Green function of a boundary scalar operator. Using a WKB approach and numerical checks, it reveals two key holographic signatures: bulk-cone singularities from interior null geodesics and gravitational echoes from waves traversing the gravastar interior, with a universal power law for the bulk-cone singularities $G_R(\omega,\ell) \sim (nT(u_*)-t)^{-\alpha-2\nu-3/2}$ and $\alpha=(d-2)/2$, $\nu=\sqrt{(d/2)^2+m^2}$. Numerical results in $d=3$ confirm these predictions and show clear echoes alongside the photon-sphere reflections, consistent with geodesic arrivals. The work discusses a path toward a CFT interpretation, potential generalizations to charged or rotating ECOs, and the implications for horizon-scale physics in holography and ECO phenomenology.

Abstract

Quantum gravity effects are expected to resolve the black hole singularity and the effects may deform the region near but outside the horizon. Applying AdS/CFT correspondence, we see their signatures from the viewpoint of dual conformal field theory. As a regularized geometry, we consider AdS gravastar constructed by gluing AdS-Schwarzschild and de Sitter spacetime. The retarded Green functions of dual conformal field theory have bulk-cone singularities associated with null trajectories in the bulk and we obtain the singularities specific to a horizon-less geometry. We also observe echoes coming from waves reflected behind the photon sphere. The existence of echoes implies the modification of geometry inside the photon sphere.

Figures (4)

• Figure 1: The potential for AdS-Schwarzschild black hole
• Figure 2: The potential for AdS gravastar
• Figure 3: The Green function $G_R(t,\pi/2)$ for the gravastar for $d=3$, $\mu=1/15$, and $r_0=1.001r_h$. We adopt the cutoff $\omega_c=\ell_c=35$ and the upper bound $\omega_\mathrm{max}=\ell_\mathrm{max}=150$. The vertical dashed lines indicate the light-cone (LC) and bulk-cone (BC) singularities.
• Figure 4: Echoes of $G_R(t,\ell)$ for the gravastar with $d=3$, $\mu=1/50$, and $r_0=1.000001r_h$. We take $\ell=1$ and $\omega_c=15$.