Gapped domain walls, gapped boundaries, and topological degeneracy.

  title={Gapped domain walls, gapped boundaries, and topological degeneracy.},
  author={Tian Lan and Juven C. Wang and Xiao-Gang Wen},
  journal={Physical review letters},
  volume={114 7},
Gapped domain walls, as topological line defects between (2+1)D topologically ordered states, are examined. We provide simple criteria to determine the existence of gapped domain walls, which apply to both Abelian and non-Abelian topological orders. Our criteria also determine which (2+1)D topological orders must have gapless edge modes, namely, which (1+1)D global gravitational anomalies ensure gaplessness. Furthermore, we introduce a new mathematical object, the tunneling matrix W, whose… 

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