Topological response of gapped fermions to a U(1)\text{U}(1) Gauge field

May 11, 2017
36 pages
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Abstract: (arXiv)
We present a detailed path integral derivation of the topological response of gapped free fermions, in 2+12+1 dimensions, to an external U(1)\text{U}(1) Gauge field. The well-known Hall response is obtained by identifying the Chern-Simons term in the effective action with the correct coefficient. We extend the result to 2d+12d+1 dimensions in which the response is associated to a Chern-Simons term with a coefficient related to a characteristic class coming from topological band theory. We comment on the bulk-to-boundary principle which arises naturally when one considers the theory on a manifold with boundary.