http://arxiv.org/abs/0710.1904 Relativistic generalization of Brownian Motion Authors: T. Koide, T. Kodama 11 pages (Submitted on 10 Oct 2007) "The relativistic generalization of the Brownian motion is discussed. We show that the transformation property of the noise term is determined by requiring for the equilibrium distribution function to be Lorentz invariant, such as the Jüttner distribution function. It is shown that this requirement generates an entanglement between the force term and the noise so that the noise itself should not be a covariant quantity." This just came out. Koide and Kodama are famous names around here, so I thought some folks might like to take note of a joint paper by the two.