Simple algebraic-group closure conjecture over the reals and p-adics

Let A\mathcal{A} be a connected commutative algebraic group over Q\mathbb{Q}, let LA(Q)\mathcal{L}\subset\mathcal{A}(\mathbb{Q}) be finitely generated, and let L\overline{\mathcal{L}} denote its closure in either A(R)\mathcal{A}(\mathbb{R}) or A(Qp)\mathcal{A}(\mathbb{Q}_p). Suppose that A\mathcal{A} is simple over Q\mathbb{Q}. Simple closure conjecture. In A(R)\mathcal{A}(\mathbb{R}), either L\mathcal{L} is discrete or L\mathcal{L} is dense. In A(Qp)\mathcal{A}(\mathbb{Q}_p), if L\mathcal{L} is contained in a maximal compact subgroup, then L\overline{\mathcal{L}} is, up to the stated identification, Zp\mathbb{Z}_p^\ell, where =min(rankL,dimA)\ell=\min(\operatorname{rank}\mathcal{L},\dim\mathcal{A}). The claim is presented as known for simple groups and for \mathcal{A}=R_{K/\mathbb{Q}(\mathbb{G}_m), but no resolution status is supplied for the conjectural assertions.

Sources & referencesView supporting material

Primary source

Dipendra Prasad, “Some questions in Diophantine approximation: real and p-adics”, arXiv:2505.15744 (2025).

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