Bulk-cone singularities & signatures of horizon formation in AdS/CFT

TL;DR

This paper explores how singularities in boundary correlation functions in AdS/CFT relate to bulk causal structures, revealing how boundary observables can signal horizon formation during gravitational collapse.

Contribution

It introduces the concept of bulk-cone singularities in boundary correlators and demonstrates their use in probing bulk geometry and horizon formation in AdS spacetime.

Findings

Bulk-cone singularities occur when boundary points are connected by bulk null geodesics.

Pattern of singularities can reveal bulk causal structure.

Signature of horizon formation appears in boundary correlators during shell collapse.

Abstract

We discuss the relation between singularities of correlation functions and causal properties of the bulk spacetime in the context of the AdS/CFT correspondence. In particular, we argue that the boundary field theory correlation functions are singular when the insertion points are connected causally by a bulk null geodesic. This implies the existence of "bulk-cone singularities" in boundary theory correlation functions which lie inside the boundary light-cone. We exhibit the pattern of singularities in various asymptotically AdS spacetimes and argue that this pattern can be used to probe the bulk geometry. We apply this correspondence to the specific case of shell collapse in AdS/CFT and indicate a sharp feature in the boundary observables corresponding to black hole event horizon formation.