Telltale traces of U(1) fields in noncommutative standard model extensions

Restrictions imposed by gauge invariance in noncommutative spaces together with the effects of ultraviolet/infrared mixing lead to strong constraints on possible candidates for a noncommutative extension of the standard model. In this paper, we consider a general class of noncommutative models consistent with these restrictions and based upon a gauge theory with the gauge group U(N1) x U(N2) x.. x U(Nm) coupled to matter fields transforming in the (anti)-fundamental, bi-fundamental and adjoint representations. We pay particular attention to overall trace-U(1) factors of the gauge group which are affected by the ultraviolet/infrared mixing. We show that, in general, these trace-U(1) gauge fields do not decouple sufficiently fast in the infrared, and lead to sizable Lorentz symmetry violating effects in the low-energy effective theory. Making these effects unobservable would require pushing the constraint on the noncommutativity mass scale far beyond the Planck mass (MNC -> 10100 MP) and severely limits the phenomenological prospects of such models. (orig.)