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Classification of 2D Fermionic Systems with a $\mathbb Z_2$ Flavor Symmetry

High Energy Physics - Theory 2026-04-13 v1 Strongly Correlated Electrons Mathematical Physics math.MP

Abstract

We classify superfusion categories describing two-dimensional fermionic systems equipped with the universal fermion-parity symmetry, implemented by a topological defect line (TDL) ZZ, and an additional Z2\mathbb{Z}_2 flavor symmetry generated by a WW TDL. Depending on whether WW is m-type or q-type, its fusion rules lead to three distinct classes, and solving the super-pentagon equations yields 16 consistent superfusion categories. These are labeled by invariants (νW,νZ,νWZ)(\nu_W,\nu_Z,\nu_{WZ}), which determine the Z8\mathbb{Z}_8 anomaly classes of the symmetries generated by WW, ZZ, and WZWZ. We also provide explicit realizations using multiple Majorana fermions and comment on implications for fermionic CFTs and gapped phases.

Keywords

Cite

@article{arxiv.2604.09503,
  title  = {Classification of 2D Fermionic Systems with a $\mathbb Z_2$ Flavor Symmetry},
  author = {Chi-Ming Chang and Jin Chen and Fengjun Xu},
  journal= {arXiv preprint arXiv:2604.09503},
  year   = {2026}
}

Comments

17 pages+4 appendices