Monodromy Defects from Hyperbolic Space

TL;DR

This paper investigates monodromy defects in $O(N)$ scalar theories using hyperbolic space methods, analyzing free and interacting cases, and explores defect RG flows and CFT data extraction techniques.

Contribution

It introduces a hyperbolic space approach to study monodromy defects, including large $N$ and $\e$-expansion analyses, and examines defect RG flows and CFT data computations.

Findings

Validation of the defect RG flow conjecture through free and interacting examples.

Development of techniques to compute defect CFT data using $S^1\times H^{d-1}$ setup.

Insights into expectation values and operator dimensions in defect theories.

Abstract

We study monodromy defects in $O(N)$ symmetric scalar field theories in $d$ dimensions. After a Weyl transformation, a monodromy defect may be described by placing the theory on $S^1\times H^{d-1}$, where $H^{d-1}$ is the hyperbolic space, and imposing on the fundamental fields a twisted periodicity condition along $S^1$. In this description, the codimension two defect lies at the boundary of $H^{d-1}$. We first study the general monodromy defect in the free field theory, and then develop the large $N$ expansion of the defect in the interacting theory, focusing for simplicity on the case of $N$ complex fields with a one-parameter monodromy condition. We also use the $\epsilon$-expansion in $d=4-\epsilon$, providing a check on the large $N$ approach. When the defect has spherical geometry, its expectation value is a meaningful quantity, and it may be obtained by computing the free energy of the twisted theory on $S^1\times H^{d-1}$. It was conjectured that the logarithm of the defect expectation value, suitably multiplied by a dimension dependent sine factor, should decrease under a defect RG flow. We check this conjecture in our examples, both in the free and interacting case, by considering a defect RG flow that corresponds to imposing alternate boundary conditions on one of the low-lying Kaluza-Klein modes on $H^{d-1}$. We also show that, adapting standard techniques from the AdS/CFT literature, the $S^1\times H^{d-1}$ setup is well suited to the calculation of the defect CFT data, and we discuss various examples, including one-point functions of bulk operators, scaling dimensions of defect operators, and four-point functions of operator insertions on the defect.