Some model theory and topological dynamics of p-adic algebraic groups

Davide Penazzi; Anand Pillay; Ningyuan Yao

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arXiv · 1704.07764

Some model theory and topological dynamics of p-adic algebraic groups

Davide Penazzi·Anand Pillay·Ningyuan Yao

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Abstract

We initiate the study of p-adic algebraic groups G from the stability-theoretic and definable topological-dynamical points of view, that is, we consider invariants of the action of G on its space of types over Q_p in the language of fields. We consider the additive and multiplicative groups of Q_p and Z_p, the group of upper triangular invertible 2\times 2 matrices, SL(2,Z_p), and, our main focus, SL(2,Q_p). In all cases we identify f-generic types (when they exist), minimal subflows, and idempotents. Among the main results is that the ``Ellis group" of SL(2,Q_p)$ is the profinite completion of Z, yielding a counterexample to Newelski's conjecture with new features: G = G^{00} = G^{000} but the Ellis group is infinite. A final section deals with the action of SL(2,Q_p) on the type-space of the projective line over Q_p.

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Davide Penazzi, Anand Pillay, Ningyuan Yao. 2017-04-25. Some model theory and topological dynamics of p-adic algebraic groups. https://arxiv.org/abs/1704.07764

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