Openness conjecture for proper and cocompact actions
Openness conjecture for proper and cocompact actions
Let be a homogeneous space of reductive type, and let be a discrete subgroup of acting properly discontinuously and cocompactly on . Write for the space of representations of in . Openness conjecture. There is a neighborhood of the natural inclusion such that every is discrete and faithful, and the action of on via is properly discontinuous and cocompact. Stability under small deformations would give openness of the space of proper and cocompact actions, a phenomenon known in important special cases but posed here in this generality.
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Sources & referencesView supporting material
Primary source
Fanny Kassel and Nicolas Tholozan, “Sharpness of proper and cocompact actions on reductive homogeneous spaces”, arXiv:2410.08179 (2026).
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