Beyond the unitarity bound in AdS/CFT_(A)dS

TL;DR

This paper explores how violations of the unitarity bound in boundary CFTs on (A)dS spacetimes manifest as ghost excitations in the bulk AdS physics, revealing insights into multi-layered AdS/CFT dualities.

Contribution

It demonstrates the bulk reflection of boundary unitarity violations via ghost modes and analyzes the impact of boundary conditions on this phenomenon in (A)dS holography.

Findings

Violations of unitarity bound correspond to ghost excitations in bulk.

Boundary conditions on AdS slices influence the bulk ghost presence.

Insights into multi-layered AdS/CFT dualities derived from boundary analysis.

Abstract

In this work we expand on the holographic description of CFTs on de Sitter (dS) and anti-de Sitter (AdS) spacetimes and examine how violations of the unitarity bound in the boundary theory are recovered in the bulk physics. To this end we consider a Klein-Gordon field on AdS_(d+1) conformally compactified such that the boundary is (A)dS_d, and choose masses and boundary conditions such that the corresponding boundary operator violates the CFT unitarity bound. The setup in which the boundary is AdS_d exhibits a particularly interesting structure, since in this case the boundary itself has a boundary. The bulk theory turns out to crucially depend on the choice of boundary conditions on the boundary of the AdS_d slices. Our main result is that violations to the unitarity bound in CFTs on dS_d and AdS_d are reflected in the bulk through the presence of ghost excitations. In addition, analyzing the setup with AdS_d on the boundary allows us to draw conclusions on multi-layered AdS/CFT-type dualities.