“…The noncommutative U (n) sigma model may be obtained by a reduction of the Nair-Schiff sigma-model-type action [32,33] from four to three dimensions, 5) where Greek indices include the extra coordinate ρ, and λµνσ denotes the totally antisymmetric tensor in R 4 . The field Φ(t, x, y) is group-valued, Φ † = Φ −1 , with an extension Φ(t, x, y, ρ) interpolating between Φ(t, x, y, 0) = const and Φ(t, x, y, 1) = Φ(t, x, y) , (2.6) and 'tr' implies the trace over the U (n) group space.…”