Chern-Simons action S_CS = (k/4π)∫Tr(A∧dA + (2/3)A∧A∧A); level-k Chern-class quantisation

Chern-Simons topological gauge theory. Setup: a 3-manifold M with a principal G-bundle (G compact semi-simple Lie group, e.g., SU(2)); connection 1-form A ∈ Ω¹(M, g). The Chern-Simons action S_CS = (k/4π)∫_M Tr(A∧dA + (2/3)A∧A∧A), integer…