Constraints from cosmic rays on non-systematic Lorentz violation
  In this article we analyze the radiation loss from a high energy cosmic ray proton propagating in a spacetime with non-systematic Lorentz violation. From an effective field theory perspective we illuminate flaws in previous attempts that use threshold approaches to analyze this problem. We argue that in general such approaches are of rather limited use when dealing with non-systematic Lorentz violating scenarios. The main issues we raise are a) the limited applicability of threshold energy conservation rules when translation invariance is broken and b) the large amounts of proton particle production due to the time dependence of the fluctuations. Ignoring particle production, we derive a constraint on the magnitude of velocity fluctuation $|v_f|<10^{-6.5}$, much weaker than has been previously argued. However, we show that in fact particle production makes any such constraint completely unreliable. 
Sayandeb Basu and David Mattingly