Published online by Cambridge University Press: 29 April 2018
This paper is concerned with factors of independent and identically distributed processes on the 
$d$-regular tree for 
$d\geq 3$. We study the mutual information of values on two given vertices. If the vertices are neighbors (i.e. their distance is 
$1$), then a known inequality between the entropy of a vertex and the entropy of an edge provides an upper bound for the (normalized) mutual information. In this paper we obtain upper bounds for vertices at an arbitrary distance 
$k$, of order 
$(d-1)^{-k/2}$. Although these bounds are sharp, we also show that an interesting phenomenon occurs here: for any fixed process, the rate of mutual information decay is much faster, essentially of order 
$(d-1)^{-k}$.