Comment on [arXiv:1106.1417] "Small Lorentz violations in quantum gravity: do they lead to unacceptably large effects?"

Abstract

A recent paper by Gambini, Rastgoo and Pullin [arXiv:1106.1417 investigates the important issue of constraints from Lorentz invariance on Planck scale physics, arguing that the classic analysis of Collins, Perez, Sudarsky, Urrutia and Vucetich \cite{cpsuv} is not generally valid. We argue that the new work is based on models that do not capture the relevant physics, and that almost all models of observable high energy Lorentz violation, and proposed Lorentz-violating theories of quantum gravity, are ruled out by low energy tests; the only known exceptions are based on supersymmetry.

Comments: 3 pages. v2: slightly expanded version, emphasizing that almost all Lorentz-violating theories are ruled out by precision tests