Tensor network approach to electromagnetic duality in (3+1)d topological gauge models

TL;DR

This paper develops tensor network representations for ground states of (3+1)d topological gauge theories, revealing electromagnetic duality through Morita equivalence of boundary conditions and connecting to known dualities in specific cases.

Contribution

It introduces a family of tensor network models for (3+1)d gauge theories with boundary conditions, demonstrating electromagnetic duality via Morita equivalence of fusion 2-categories.

Findings

Tensor network representations for (3+1)d gauge theories with boundary conditions.

Explicit Morita equivalence between 2Vec_G and 2Rep(G).

Connection between electromagnetic duality and Kramers-Wannier duality in special cases.

Abstract

Given the Hamiltonian realisation of a topological (3+1)d gauge theory with finite group $G$, we consider a family of tensor network representations of its ground state subspace. This family is indexed by gapped boundary conditions encoded into module 2-categories over the input spherical fusion 2-category. Individual tensors are characterised by symmetry conditions with respect to non-local operators acting on entanglement degrees of freedom. In the case of Dirichlet and Neumann boundary conditions, we show that the symmetry operators form the fusion 2-categories $\mathsf{2Vec}_G$ of $G$-graded 2-vector spaces and $\mathsf{2Rep}(G)$ of 2-representations of $G$, respectively. In virtue of the Morita equivalence between $\mathsf{2Vec}_G$ and $\mathsf{2Rep}(G)$ -- which we explicitly establish -- the topological order can be realised as the Drinfel'd centre of either 2-category of operators; this is a realisation of the electromagnetic duality of the theory. Specialising to the case $G = \mathbb Z_2$, we recover tensor network representations that were recently introduced, as well as the relation between the electromagnetic duality of a pure (3+1)d $\mathbb Z_2$ gauge theory and the Kramers-Wannier duality of a boundary (2+1)d Ising model.