Definably Topological Dynamics of $p$-Adic Algebraic Groups

Abstract: We study the $p$-adic algebraic groups $G$ from the definable topological-dynamical point of view. We consider the case that $M$ is an arbitrary $p$-adic closed field and $G$ an algebraic group over ${\mathbb Q}_p$ admitting an Iwasawa decompostion $G=KB$, where $K$ is open and definably compact over ${\mathbb Q}_p$, and $B$ is a borel subgroup of $G$ over ${\mathbb Q}_p$. Our main result is an explicit description of the minimal subflow and Ellis Group of the universal definable $G(M)$-flow $S_G(M^{\text{ext}})$. We prove that the Ellis group of $S_G(M^{\text{ext}})$ is isomorphic to the Ellis group of $S_B(M^{\text{ext}})$, which is $B/B^0$. As applications, we conclude that the Ellis groups corresponding to $\text{GL}(n,M)$ and $\text{SL}(n,M)$ are isomorphic to $(\hat {\mathbb Z} \times {\mathbb Z}_p^*)^n$ and $(\hat {\mathbb Z} \times {\mathbb Z}_p^*)^{n-1}$ respectively, generalizing the main result of Penazzi, Pillay, and Yao in Some model theory and topological dynamics of $p$-adic algebraic groups, Fundamenta Mathematicae, 247 (2019), pp. 191--216.