2026/07/26 by Zhentao Zhang
#math.LO
We prove that every group G definable in the pure p-adic field ℚp is weakly regular. We show that every one-parameter subgroup is definable. We also show that its one-parameter core Gu, together with a suitable regular open subgroup GΩ, is definable. Finally, we show that if H is a dfg component of G, then Gu=⟨(Hg)u:g∈ G⟩. In fact, Gu is a finite product of the one-parameter cores of finitely many conjugates of H. In particular, when G is definably amenable, Gu=Hu.