Symmetries of the KMS simplex

A continuous groupoid homomorphism $c$ on a locally compact second countable Hausdorff 'etale groupoid $\mathcal{G}$ gives rise to a $C^{\ast }$-dynamical system in which every $\beta$-KMS state can be associated to a $e^{-\beta c}$-quasi-invariantmeasure$\mu$on$$\mathcal{G}$^{(0)}$\mathrm{.}Letting$\Delta_{\mu}$denotethesetofKMSstatesassociatedtosucha$\mu$, we will prove that ${\mathrm{\Delta }}_{\mu }$ is a simplex for a large class of groupoids, and we will show that there is an abelian group that acts transitively and freely on the extremal points of ${\mathrm{\Delta }}_{\mu }$. This group can be described using the support of $\mu$, so our theory of symmetries can be used to obtain a description of all KMS states by describing the $e^{-\beta c}$-quasi-invariant measures. To illustrate this we will describe the KMS states for the Cuntz-Krieger algebras of all finite higher rank graphs without sources and a large class of continuous one-parameter groups.