Additive realizations of asymptotically additive set maps

TL;DR

This paper investigates conditions under which set maps into Banach spaces can be realized as ergodic sums of vectors under group representations, extending previous work and connecting additive and asymptotically additive frameworks.

Contribution

It characterizes when set maps can be realized as ergodic sums for uniformly bounded group representations, extending prior results to broader classes of maps and group actions.

Findings

Characterization of bounded asymptotically additive set maps

Extension of realization results to group representations

Generalization of thermodynamic formalism concepts

Abstract

Given a countable discrete amenable group, we study conditions under which a set map into a Banach space (or more generally, a complete semi-normed space) can be realized as the ergodic sum of a vector under a group representation, such that the realization is asymptotically indistinguishable from the original map. We show that for uniformly bounded group representations, this property is characterized by the class of bounded asymptotically additive set maps, extending previous work for sequences in Banach spaces and on the case of a single non-expansive linear map. Additionally, we develop a relative version of this characterization, identifying when the additive realization can be chosen within a prescribed target set. As an application, our results generalize central aspects of thermodynamic formalism, bridging the additive and asymptotically additive frameworks.