Entanglement branes and factorization in conformal field theory

TL;DR

This paper explores how to factorize states in 2D conformal field theory using path integral processes and cobordisms, revealing connections to edge modes, symmetry algebra co-products, and Bogoliubov transformations.

Contribution

It introduces a novel entanglement boundary condition in CFT, linking state factorization to cobordisms and symmetry algebra co-products, with implications for understanding edge modes.

Findings

Reduced density matrices include super-selection sectors.

Factorization relates to the co-product of the symmetry algebra.

In free bosons, the factorization map is a Bogoliubov transformation.

Abstract

In this work, we consider the question of local Hilbert space factorization in 2D conformal field theory. Generalizing previous work on entanglement and open-closed TQFT, we interpret the factorization of CFT states in terms of path integral processes that split and join the Hilbert spaces of circles and intervals. More abstractly, these processes are cobordisms of an extended CFT which are defined purely in terms of the OPE data. In addition to the usual sewing axioms, we impose an entanglement boundary condition that is satisfied by the vacuum Ishibashi state. This choice of entanglement boundary state leads to reduced density matrices that sum over super-selection sectors, which we identify as the CFT edge modes. Finally, we relate our factorization map to the co-product formula for the CFT symmetry algebra, which we show is equivalent to a Boguliubov transformation in the case of a free boson.