Quantized topological terms in weak-coupling gauge theories with a global symmetry and their connection to symmetry-enriched topological phases

Dec, 2012
13 pages
Published in:
  • Phys.Rev.B 87 (2013) 16, 165107
  • Published: Apr 5, 2013
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Abstract: (APS)
We study the quantized topological terms in a weak-coupling gauge theory with gauge group Gg and a global symmetry Gs in d space-time dimensions. We show that the quantized topological terms are classified by a pair (G,νd), where G is an extension of Gs by Gg and νd an element in group cohomology Hd(G,R/Z). When d=3 and/or when Gg is finite, the weak-coupling gauge theories with quantized topological terms describe gapped symmetry enriched topological (SET) phases (i.e., gapped long-range-entangled phases with symmetry). Thus, those SET phases are classified by Hd(G,R/Z), where G/Gg=Gs. We also apply our theory to a simple case Gs=Gg=Z2, which leads to 12 different SET phases in 2+1 dimensions [(2+1)D], where quasiparticles have different patterns of fractional Gs=Z2 quantum numbers and fractional statistics. If the weak-coupling gauge theories are gapless, then the different quantized topological terms may describe different gapless phases of the gauge theories with a symmetry Gs, which may lead to different fractionalizations of Gs quantum numbers and different fractional statistics [if in (2+1)D].
Note:
  • 13 pages, 2 figures, PRB accepted version with added clarification on obtaining G_s charge for a given PSG with non-trivial topological terms. arXiv admin note: text overlap with arXiv:1301.7675
  • 71.27.+a
  • 02.40.Re
  • quantization: topological
  • gauge field theory: weak coupling
  • statistics: fractional
  • phase: topological
  • symmetry: global
  • quantum number
  • cohomology
  • any-dimensional