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Limit points and additive group actions

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Abstract

We show that an effective action of the one-dimensional torus \({\mathbb G}_m\) on a normal affine algebraic variety X can be extended to an effective action of a semi-direct product \({\mathbb G}_m\rightthreetimes {\mathbb G}_a\) with the same general orbit closures if and only if there is a divisor D on X that consists of \({\mathbb G}_m\)-fixed points. This result is applied to the study of orbits of the automorphism group \({{\,\mathrm{Aut}\,}}(X)\) on X.

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Acknowledgements

The author is grateful to Alvaro Liendo for a fruitful discussion, and to Sergey Gaifullin, Michail Zaidenberg, and two anonymous reviewers for many useful comments, suggestions and references to related results.

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Correspondence to Ivan Arzhantsev.

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The research was supported by Russian Science Foundation, Grant 19-11-00056.

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Arzhantsev, I. Limit points and additive group actions. Ricerche mat 73, 715–724 (2024). https://doi.org/10.1007/s11587-021-00630-z

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  • DOI: https://doi.org/10.1007/s11587-021-00630-z

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