Reference:

Topological gauge theories and group cohomology

Robbert Dijkgraaf and Edward Witten

http://projecteuclid.org/DPubS?service=UI&version=1.0&verb=Display&handle=euclid.cmp/1104180750



Braiding statistics approach to symmetry-protected topological phases

Michael Levin, Zheng-Cheng Gu

http://arxiv.org/abs/1202.3120