On intrinsic ergodicity and weakenings of the specification property

Abstract: Since seminal work of Bowen, it has been known that the specification property implies various useful properties about a topological dynamical system, among them uniqueness of the measure of maximal entropy (often referred to as intrinsic ergodicity). Weakenings of the specification property called almost weak specification and almost specification have been defined and profitably applied in various works. However, it has been an open question whether either or both of these properties imply intrinsic ergodicity. We answer this question negatively by exhibiting examples of subshifts with multiple measures of maximal entropy with disjoint support which have almost weak specification with any gap function $f(n) = O(\ln n)$ or almost specification with any mistake function $g(n) \geq 4$. We also show some results in the opposite direction, showing that subshifts with almost weak specification with gap function $f(n) = o(\ln n)$ or almost specification with mistake function $g(n) = 1$ cannot have multiple measures of maximal entropy with disjoint support.