The precise geometric fibration conjecture for compact quotients

Let G/HG/H be a reductive homogeneous space, with maximal compact subgroup KK. Let πH:G/KHG/H\pi_H:G/K_H\to G/H and πK:G/KHG/K\pi_K:G/K_H\to G/K be the natural projections, and let dim+(G/H)\dim_+(G/H) denote the dimension specified in the source. Let Γ\Gamma be a torsion-free subgroup of GG acting properly discontinuously and cocompactly on G/HG/H.

Precise geometric fibration conjecture. There exists a Γ\Gamma-invariant contractible smooth submanifold M~\widetilde{M} of G/KG/K, of dimension dim+(G/H)\dim_+(G/H), such that

G/H=m~M~πHπK1(m~).G/H=\bigsqcup_{\widetilde{m}\in\widetilde{M}}\pi_H\circ\pi_K^{-1}(\widetilde{m}).

This is presented as a more precise form of the geometric fibration conjecture. The relation between compact quotients and the proposed fibration structure remains open in general.

Sources & referencesView supporting material

Primary source

Fanny Kassel, Yosuke Morita and Nicolas Tholozan, “Compact quotients of homogeneous spaces and homotopy theory of sphere bundles”, arXiv:2601.05857 (2026).

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