Protected operators in non-local defect CFTs from AdS

TL;DR

This paper demonstrates that protected defect operators exist in non-local boundary CFTs from AdS, due to a Goldstone mechanism, even without local stress tensors or conserved currents.

Contribution

It introduces a Goldstone-type mechanism explaining protected defect operators in non-local AdS boundary theories, independent of traditional local CFT arguments.

Findings

Protected displacement and tilt operators have conserved quantum numbers.

The mechanism is illustrated in various models including Maxwell and Yang--Mills theories in AdS.

Defect-induced symmetry breaking is spontaneous from the bulk perspective.

Abstract

For a local quantum field theory in anti-de Sitter space with conformal boundary conditions but without dynamical gravity, the boundary theory is generically a non-local conformal field theory. Such theories can support conformal defects, but the standard local-CFT arguments based on a boundary stress tensor and conserved currents do not apply. We argue that, under general assumptions, displacement and tilt operators nevertheless exist and have protected quantum numbers. The mechanism is a Goldstone-type phenomenon in AdS: defect-induced symmetry breaking on the boundary is spontaneous from the viewpoint of the local bulk theory, whose Ward identities enforce the corresponding protected defect operators. We illustrate the mechanism in weakly coupled defect RG flows, long-range Landau--Ginzburg models, 4D Maxwell theory, and Yang--Mills theory in AdS.