Boundary states in the SU(2)$_k$ WZW model from open string field theory

TL;DR

This paper uses open string field theory to analyze boundary states in the SU(2)$_k$ WZW model, discovering solutions that correspond to various boundary conditions, including symmetric, complex, and symmetry-breaking states.

Contribution

It develops algorithms for effective calculation of the action and identifies new classical solutions representing different boundary states in the model.

Findings

Real solutions correspond to maximally symmetric Cardy boundary states.

Complex solutions describe SL(2,ℂ) boundary conditions.

Exotic solutions include symmetry-breaking boundary states.

Abstract

We analyze boundary states in the SU(2)$_k$ WZW model using open string field theory in the level truncation approximation. We develop algorithms that allow effective calculation of action in this model and we search for classical solutions of the equations of motion, which are conjectured to describe boundary states. We find three types of solutions. First, there are real solutions that represent maximally symmetric Cardy boundary states and we show that they satisfy certain selection rules regarding their SU(2) parameters. Next, we find complex solutions that go beyond the SU(2) model and describe maximally symmetric SL(2,$\mathbb C$) boundary conditions. Finally, we find exotic solutions that correspond to symmetry-breaking boundary states. Most of real exotic solutions describe the so-called B-brane boundary states, but some may represent yet unknown boundary states.