Geodesically Complete Metrics Induce Boundary Non-locality in Holography: Consequences for the Entanglement Entropy

TL;DR

This paper demonstrates that geodesically complete metrics in AdS/CFT induce boundary non-local operators, affecting entanglement entropy calculations, and shows how brane structures can resolve these non-localities.

Contribution

It explicitly links boundary non-locality in holography to geodesically complete metrics and proposes that true entanglement entropy should be computed in full 10-dimensional spacetime.

Findings

Boundary operators become fractional Laplacians in complete metrics.

Non-locality vanishes with incomplete or brane-structured metrics.

Entanglement entropy is bounded by brane placement and should be computed in 10D spacetime.

Abstract

We show explicitly that the full structure of IIB string theory is needed to remove the non-localities that arise in boundary conformal theories that border hyperbolic spaces on AdS$_5$. Specifically, using the Caffarelli/Silvestri\cite{caffarelli}, Graham/Zworski\cite{graham}, and Chang/Gonzalez\cite{chang:2010} extension theorems, we prove that the boundary operator conjugate to bulk p-forms with negative mass in geodesically complete metrics is inherently a non-local operator, specifically the fractional conformal Laplacian. The non-locality, which arises even in compact spaces, applies to any degree p-form such as a gauge field. We show that the boundary theory contains fractional derivatives of the longitudinal components of the gauge field if the gauge field in the bulk along the holographic direction acquires a mass via the Higgs mechanism. The non-locality is shown to vanish once the metric becomes incomplete, for example, either 1) asymptotically by adding N transversely stacked Dd-branes or 2) exactly by giving the boundary a brane structure and including a single transverse Dd-brane in the bulk. The original Maldacena conjecture within IIB string theory corresponds to the former. In either of these proposals, the location of the Dd-branes places an upper bound on the entanglement entropy because the minimal bulk surface in the AdS reduction is ill-defined at a brane interface. Since the brane singularities can be circumvented in the full 10-dimensional spacetime, we conjecture that the true entanglement entropy must be computed from the minimal surface in 10-dimensions, which is of course not minimal in the AdS$_5$ reduction.