Spontaneous reduction of noncommutative gauge symmetry and model building

We propose a mechanism for the spontaneous (gauge-invariant) reduction of noncommutative U(n) gauge theories down to SU(n). This can be achieved through the condensation of composite U(n) gauge invariant fields that involve half-infinite Wilson lines in the trace-U(1) noninvariant and SU(n) preserving direction. Based on this mechanism, we discuss an anomaly-free fully gauge invariant noncommutative standard model based on the minimal gauge group U(3) x U(2) x U(1), previously proposed, and show how it can be consistently reduced to the standard model with the usual particle spectrum. Charge quantization for quarks and leptons naturally follows from the model. (orig.)