Ergodic Average Dominance for Unimodular Amenable Groups

Abstract

In this paper we show that the ergodic averages of the action of any unimodular amenable group along certain Følner sequences can be dominated by the Cesàro means of a suitably constructed Markov operator, that is, the ergodic averages of an integer action. Moreover, the restriction on these Følner sequences are mild enough so that every two-sided Følner sequence has a subsequence satisfying these conditions. As a consequence of this inequality, we obtain the maximal and pointwise (individual) ergodic theorems for actions of unimodular amenable groups directly from the corresponding ergodic theorems for integer actions. This allows us to deal with the commutative and noncommutative ergodic theorems on an equal footing.