Small Lorentz violations in quantum gravity: do they lead to unacceptably large effects?

We discuss the applicability of the argument of Collins, Pérez, Sudarsky, Urrutia and Vucetich to loop quantum gravity. This argument suggests that Lorentz violations, even ones that only manifest themselves at energies close to the Planck scale, have significant observational consequences at low energies when one considers perturbative quantum field theory and renormalization. We show that non-perturbative treatments like those of loop quantum gravity may generate deviations of Lorentz invariance of a different type than those considered by Collins et al (2004 Phys. Rev. Lett. 93 191301) that do not necessarily imply observational consequences at low energy. © 2011 IOP Publishing Ltd.