  Because of ultraviolet/infrared (UV/IR) mixing, the low energy physics of
noncommutative gauge theories in the Moyal-Weyl approach seems to depend
crucially on the details of the ultraviolet completion. However, motivated by
recent string theory analyses, we argue that their phenomenology with a very
general class of UV completions can be accurately modelled by a cutoff close to
the Planck scale. In the infrared the theory tends continuously to the
commutative gauge theory. If the photon contains contributions from a
trace-U(1), we would observe vacuum birefringence, i.e. a polarisation
dependent propagation speed, as a residual effect of the noncommutativity.
Constraints on this effect require the noncommutativity scale to be close to
the Planck scale.
