Non-rigidity conjecture for real projective spaces

Let n4n\geqslant 4 and let GPGLn+1(R)G\subset\mathrm{PGL}_{n+1}(\mathbb{R}) be a finite subgroup. The projective space PRn\mathbb{P}^n_{\mathbb{R}} is called GG-birationally rigid when it is birationally rigid with respect to the action of GG.

Non-rigidity conjecture. For every n4n\geqslant 4 and every finite subgroup GPGLn+1(R)G\subset\mathrm{PGL}_{n+1}(\mathbb{R}), PRn\mathbb{P}^n_{\mathbb{R}} is not GG-birationally rigid.

The conjecture extends the theorem established in the paper for n{4,5,6}n\in\{4,5,6\} and predicts non-rigidity for all higher-dimensional real projective spaces. The context states that no examples of finite groups yielding GG-birational rigidity are known in the corresponding complex dimensions n5n\geqslant 5, so the general assertion remains open.

Sources & referencesView supporting material

Primary source

Ivan Cheltsov, Frederic Mangolte and Constantin Shramov, “On G-birational rigidity of projective spaces”, arXiv:2604.20427 (2026).

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