Compact-action infinitesimal containment conjecture

Let GG be a compact group with Haar probability measure μ\mu, let ρ ⁣:ΓG\rho\colon\Gamma\to G be a homomorphism, and let Γ\Gamma act on (G,μ)(G,\mu) by γg=ρ(γ)g\gamma g=\rho(\gamma)g. For each conjugacy class of closed subgroups HGH\subset G with empty interior, let (ZH,τH)(Z_H,\tau_H) be an auxiliary probability-measure-preserving action. Compact-action infinitesimal containment conjecture.

(G,μ)infHG[Γ/ρ1(H)×(ZH,τH)].(G,\mu)\xhookrightarrow{\operatorname{inf}}\bigsqcup_{H\subset G}\left[\Gamma/\rho^{-1}(H)\times(Z_H,\tau_H)\right].

The conjecture is motivated by obstructions coming from the actions Γ/ρ1(H)\Gamma/\rho^{-1}(H) and is explicitly described by the authors as more a question than an established conjecture; no resolution is given.

Sources & referencesView supporting material

Primary source

Mikołaj Frączyk, “Infinitesimal containment and sparse factors of iid”, arXiv:2512.09301 (2025).

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