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Deformations of \(\mathbb A^1\)-fibrations. (English) Zbl 1326.14146

Cheltsov, Ivan (ed.) et al., Automorphisms in birational and affine geometry. Papers based on the presentations at the conference, Levico Terme, Italy, October 29 – November 3, 2012. Cham: Springer (ISBN 978-3-319-05680-7/hbk; 978-3-319-05681-4/ebook). Springer Proceedings in Mathematics & Statistics 79, 327-361 (2014).
Summary: Let \(B\) be an integral domain which is finitely generated over a subdomain \(R\) and let \(D\) be an \(R\)-derivation on \(B\) such that the induced derivation \(D_{\mathfrak m}\) on \(B\otimes_RR/\mathfrak m\) is locally nilpotent for every maximal ideal \(\mathfrak m\). We ask if \(D\) is locally nilpotent. Theorem 2.1 asserts that this is the case if \(B\) and \(R\) are affine domains. We next generalize the case of \(G_a\)-action treated in Theorem 2.1 to the case of \(\mathbb A^1\)-fibrations and consider the log deformations of affine surfaces with \(\mathbb A^1\)-fibrations. The case of \(\mathbb A^1\)-fibrations of affine type behaves nicely under log deformations, while the case of \(\mathbb A^1\)-fibrations of complete type is more involved (see [A. Dubouloz and T. Kishimoto, Bull. Soc. Math. Fr. 143, No. 2, 383–401 (2015; Zbl 1327.14196)]. As a corollary, we prove the generic triviality of \(\mathbb A^2\)-fibration over a curve and generalize this result to the case of affine pseudo-planes of \(\mathrm{ML}_0\)-type under a suitable monodromy condition.
For the entire collection see [Zbl 1291.14005].

MSC:

14R20 Group actions on affine varieties
14R25 Affine fibrations

Citations:

Zbl 1327.14196

References:

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