Multiple phase transitions on compact symbolic systems

Abstract

Let $\phi:X\to \mathbb R$ be a continuous potential associated with a symbolic dynamical system $T:X\to X$ over a finite alphabet. Introducing a parameter $\beta>0$ (interpreted as the inverse temperature) we study the regularity of the pressure function $\beta\mapsto P_{\rm top}(\beta\phi)$ on an interval $[\alpha,\infty)$ with $\alpha>0$. We say that $\phi$ has a phase transition at $\beta_0$ if the pressure function $P_{\rm top}(\beta\phi)$ is not differentiable at $\beta_0$. This is equivalent to the condition that the potential $\beta_0\phi$ has two (ergodic) equilibrium states with distinct entropies. For any $\alpha>0$ and any increasing sequence of real numbers $(\beta_n)$ contained in $[\alpha,\infty)$, we construct a potential $\phi$ whose phase transitions in $[\alpha,\infty)$ occur precisely at the $\beta_n$'s. In particular, we obtain a potential which has a countably infinite set of phase transitions.