Quantum Gravity Phenomenology, Lorentz Invariance and Discreteness

Abstract

Contrary to what is often stated, a fundamental spacetime discreteness need not contradict Lorentz invariance. A causal set's discreteness is in fact locally Lorentz invariant, and we recall the reasons why. For illustration, we introduce a phenomenological model of massive particles propagating in a Minkowski spacetime which arises from an underlying causal set. The particles undergo a Lorentz invariant diffusion in phase space, and we speculate on whether this could have any bearing on the origin of high energy cosmic rays.Comment: 13 pages. Replaced version with corrected fundamental solution, missing m's (mass) and c's (speed of light) added and reference on diffusion on the three sphere changed. Note with additional references added and addresses updated, as in published versio