Holographic torus entanglement and its RG flow

TL;DR

This paper investigates universal, regulator-independent entanglement entropy contributions in holographic CFTs on tori, analyzing their behavior under RG flow and proposing a renormalized EE that decreases monotonically with relevant deformations.

Contribution

It introduces a new renormalized entanglement entropy for holographic CFTs on tori that captures universal features and obeys a monotonic RG flow, extending the understanding of EE in topologically non-trivial settings.

Findings

The universal EE term reduces to a shape-independent constant in the thin torus limit.

The renormalized EE decreases monotonically under relevant deformations.

Discussion of non-uniqueness of renormalized EE in different dimensions.

Abstract

We study the universal contributions to the entanglement entropy (EE) of 2+1d and 3+1d holographic conformal field theories (CFTs) on topologically non-trivial manifolds, focusing on tori. The holographic bulk corresponds to AdS-soliton geometries. We characterize the properties of these regulator-independent EE terms as a function of both the size of the cylindrical entangling region, and the shape of the torus. In 2+1d, in the simple limit where the torus becomes a thin 1d ring, the EE reduces to a shape-independent constant $2\gamma$. This is twice the EE obtained by bipartitioning an infinite cylinder into equal halves. We study the RG flow of $\gamma$ by defining a renormalized EE that 1) is applicable to general QFTs, 2) resolves the failure of the area law subtraction, and 3) is inspired by the F-theorem. We find that the renormalized $\gamma$ decreases monotonically when the holographic CFT is deformed by a relevant operator for all allowed scaling dimensions. We also discuss the question of non-uniqueness of such renormalized EEs both in 2+1d and 3+1d.