Vacuum Structure, Lorentz Symmetry and Superluminal Particles

Abstract

If textbook Lorentz invariance is actually a property of the equations describing a sector of the excitations of vacuum above some critical distance scale, several sectors of matter with different critical speeds in vacuum can coexist and an absolute rest frame (the vacuum rest frame) may exist without contradicting the apparent Lorentz invariance felt by "ordinary" particles (particles with critical speed in vacuum equal to $c$ , the speed of light). The sectorial Lorentz symmetry may be only a low-energy limit, in the same way as the relation $ω$ (frequency) = $c_s$ (speed of sound) $k$ (wave vector) holds for low-energy phonons in a crystal. We study the consequences of such a scenario, using an ansatz inspired by the Bravais lattice as a model for some vacuum properties. It then turns out that: a) the Greisen-Zatsepin-Kuzmin cutoff on high-energy cosmic protons and nuclei does no longer apply; b) high-momentum unstable particles have longer lifetimes than expected with exact Lorentz invariance, and may even become stable at the highest observed cosmic ray energies or slightly above. Some cosmological implications of superluminal particles are also discussed.