Causal Baryon Diffusion and Colored Noise for Heavy Ion Collisions
  We construct a model for baryon diffusion which has the desired properties of analyticity and causality. The model also has the desired property that the noise correlation function is not a Dirac delta function in space and time. The model depends on three time constants in addition to the diffusion constant. This description can be incorporated into 2nd order viscous hydrodynamical models of heavy ion collisions. 
J. I. Kapusta and C. Young
nucl-th