On entropy of dynamical systems with almost specification

TL;DR

This paper constructs examples of shift spaces with almost specification that have multiple measures of maximal entropy, and explores the relationships between various specification properties and ergodic measures in dynamical systems.

Contribution

It provides new examples of shift spaces with almost specification and multiple measures of maximal entropy, and analyzes the implications of different specification properties on ergodic measures.

Findings

Constructed shift spaces with almost specification and multiple measures of maximal entropy.

Proved that certain conditions for intrinsic ergodicity are optimal.

Showed that weak specification does not imply or follow from almost specification.

Abstract

We construct a family of shift spaces with almost specification and multiple measures of maximal entropy. This answers a question from Climenhaga and Thompson [Israel J. Math. 192 (2012), no. 2, 785--817]. Elaborating on our examples we also prove that some sufficient conditions for every subshift factor of a shift space to be intrinsically ergodic given by Climenhaga and Thompson are in some sense best possible, moreover, the weak specification property neither implies intrinsic ergodicity, nor follows from almost specification. We also construct a dynamical system with the weak specification property, which does not have the almost specification property. We prove that the minimal points are dense in the support of any invariant measure of a system with the almost specification property. Furthermore, if a system with almost specification has an invariant measure with non-trivial support, then it also has uniform positive entropy over the support of any invariant measure and can not be minimal.