Concentration and local smoothness of the averaging process

Abstract

We consider the averaging process on the discrete $d$-dimensional torus. On this graph, the process is known to converge to equilibrium on diffusive timescales, not exhibiting cutoff. In this work, we refine this picture in two ways. Firstly, we prove a concentration phenomenon of the averaging process around its mean, occurring on a shorter timescale than the one of its relaxation to equilibrium. Secondly, we establish sharp gradient estimates, which capture its fast local smoothness property. This is the first setting in which these two features of the averaging process -- concentration and local smoothness -- can be quantified. These features carry useful information on a number of large scale properties of the averaging process. As an illustration of this fact, we determine the limit profile of its distance to equilibrium and derive a quantitative hydrodynamic limit for it. Finally, we discuss their implications on cutoff for the binomial splitting process, the particle analogue of the averaging process.