Have we tested Lorentz invariance enough?
  Motivated by ideas from quantum gravity, Lorentz invariance has undergone many stringent tests over the past decade and passed every one. Since there is no conclusive reason from quantum gravity that the symmetry \textit{must} be violated at some point we should ask the questions: a) are the existing tests sufficient that the symmetry is already likely exact at the Planck scale? b) Are further tests simply blind searches for new physics without reasonable expectation of a positive signal? Here we argue that the existing tests are not quite sufficient and describe some theoretically interesting areas of existing parameterizations for Lorentz violation in the infrared that are not yet ruled out but are accessible (or almost accessible) by current experiments. We illustrate this point using a vector field model for Lorentz violation containing operators up to mass dimension six and analyzing how terrestrial experiments, neutrino observatories, and Auger results on ultra-high energy cosmic rays limit this model. 
David Mattingly