Recognition: unknown
Solvable Automorphism Groups of Varieties
Pith reviewed 2026-05-14 17:53 UTC · model grok-4.3
The pith
Solvable subgroups of automorphism groups on quasi-affine varieties are algebraic when generated by irreducible families containing the identity.
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
Core claim
Let X be a variety of dimension n. When X is quasi-affine, a solvable subgroup of Aut(X) generated by an irreducible family of automorphisms containing the identity is an algebraic subgroup. Every connected solvable subgroup of Aut(X) is contained in a Borel subgroup and its derived length is at most n+1. The notions of solvable and unipotent radicals are well-defined for any subgroup of Aut(X). If X is quasi-affine and connected and B is a Borel of derived length n+1, then X is isomorphic to affine n-space and B is conjugate to the Jonquières subgroup.
What carries the argument
The irreducible family of automorphisms containing the identity that generates a solvable subgroup of Aut(X), which the argument shows must be algebraic.
If this is right
- Every connected solvable subgroup of Aut(X) lies inside some Borel subgroup.
- The derived length of any such subgroup is at most the dimension n plus one.
- Solvable and unipotent radicals are well-defined for arbitrary subgroups of Aut(X).
- A Borel subgroup of derived length exactly n+1 on a connected quasi-affine X forces X to be affine n-space with the Borel conjugate to the Jonquières subgroup.
Where Pith is reading between the lines
- The algebraicity result supplies a uniform way to attach algebraic-group invariants to automorphism groups of varieties.
- The derived-length bound suggests examining whether similar length controls hold for solvable subgroups of birational automorphism groups.
- Low-dimensional cases such as surfaces offer direct tests of whether the maximal derived length is achieved only on affine space.
Load-bearing premise
The family generating the solvable subgroup is irreducible in the algebraic sense and contains the identity.
What would settle it
A concrete counterexample would be a quasi-affine variety X together with a solvable non-algebraic subgroup of Aut(X) generated by an irreducible family containing the identity.
read the original abstract
Let $X$ be a variety of dimension $n$, and let $\mathrm{Aut}(X)$ be its automorphism group. When $X$ is quasi-affine, we prove that a solvable subgroup of $\mathrm{Aut}(X)$ that is generated by an irreducible family of automorphisms containing the identity is an algebraic subgroup. Our main applications concern arbitrary varieties. First, every connected solvable subgroup of $\mathrm{Aut}(X)$ is contained in a Borel subgroup and its derived length is $\leq n+1$. Second, the notion of solvable and unipotent radicals are well defined for any subgroup of $\mathrm{Aut}(X)$. Third, if $X$ is quasi-affine and connected and $\mathcal{B} \subset \mathrm{Aut}(X)$ is a Borel subgroup of derived length $n+1$, then $X$ is isomorphic to the affine $n$-space $\mathbb{A}^n$ and $\mathcal{B}$ is conjugate to the Jonqui\`eres subgroup.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper proves that if X is a quasi-affine variety of dimension n, then any solvable subgroup of Aut(X) generated by an irreducible family of automorphisms containing the identity is itself an algebraic subgroup. For arbitrary varieties it shows that every connected solvable subgroup of Aut(X) lies in some Borel subgroup and has derived length at most n+1; that solvable and unipotent radicals are therefore well-defined for any subgroup of Aut(X); and that if X is quasi-affine and connected and admits a Borel subgroup of derived length exactly n+1, then X is isomorphic to affine n-space and the Borel is conjugate to the Jonquières subgroup.
Significance. If the arguments are complete, the results supply a useful structure theory for automorphism groups of varieties that parallels the classical theory of algebraic groups. The characterization of affine space by the existence of a Borel of maximal derived length is a clean and potentially useful criterion. The proofs appear to rest on standard definitions of algebraic groups and varieties with no evident circularity or free parameters.
minor comments (3)
- [Abstract] The base field is never stated in the abstract or the provided statements; the results are presumably intended for algebraically closed fields of characteristic zero, but this should be made explicit in the introduction and in the statements of the main theorems.
- [Introduction] The Jonquières subgroup is invoked without a definition or reference; a brief recollection or citation in the introduction would improve readability for readers outside the immediate area.
- [Section 2] The notion of an 'irreducible family of automorphisms' is central to the first theorem but is not defined in the excerpt; a precise definition (e.g., in terms of a morphism from an irreducible variety to Aut(X)) should appear before the statement of Theorem 1.
Simulated Author's Rebuttal
We thank the referee for the positive assessment of our manuscript and the recommendation for minor revision. The referee's summary correctly captures the main theorems. No major comments were raised in the report, so we have no specific points to address point-by-point at this stage. We will make the minor revisions as needed in the next version.
Circularity Check
No circularity detected in derivation chain
full rationale
The paper's core claims (solvable subgroups generated by irreducible families are algebraic when X is quasi-affine; connected solvable subgroups lie in Borel subgroups with derived length ≤ n+1; maximal derived length forces X ≅ A^n) are stated as theorems resting on standard definitions of Aut(X), algebraic groups, irreducibility in the Zariski topology, and Borel subgroups. No load-bearing step reduces by definition or self-citation to a fitted parameter, renamed ansatz, or prior result by the same authors. The derivation chain is self-contained against external benchmarks in algebraic geometry.
Axiom & Free-Parameter Ledger
axioms (2)
- standard math Algebraic varieties and their automorphism groups are defined over an algebraically closed field of characteristic zero
- domain assumption An irreducible family of automorphisms is parametrized by an irreducible algebraic variety containing the identity
Reference graph
Works this paper leans on
- [1]
-
[2]
Grothendieck, Alexander and Raynaud, Mich. Rev\^. 2003 , bdsk-url-1 =
work page 2003
-
[3]
Modern Algebra, Volume 2: Groups and Algebras , series =
Hanspeter Kraft and Mikhail Zaidenberg , title =. Modern Algebra, Volume 2: Groups and Algebras , series =. 2025 , publisher =
work page 2025
-
[4]
Mumford, D. and Fogarty, J. and Kirwan, F. , date-added =. Geometric invariant theory , url =. 1994 , bdsk-url-1 =
work page 1994
-
[5]
Equivariant completion , volume =
Sumihiro, Hideyasu , date-added =. Equivariant completion , volume =. J. Math. Kyoto Univ. , keywords =. 1974 , zbl =. doi:10.1215/kjm/1250523277 , fjournal =
-
[6]
Introduction to actions of algebraic groups , url =
Brion, Michel , booktitle =. Introduction to actions of algebraic groups , url =. 2010 , bdsk-url-1 =. doi:10.5802/ccirm.1 , language =
- [7]
-
[8]
On the geometry of automorphism groups of affine varieties , year =
Furter, Jean-Philippe and Kraft, Hanspeter , date-added =. On the geometry of automorphism groups of affine varieties , year =
- [9]
-
[10]
Geometry of absolutely admissible representations , year =
Igusa, Jun-ichi , booktitle =. Geometry of absolutely admissible representations , year =
-
[11]
Grothendieck, Alexander , date-added =. Inst. Hautes \'Etudes Sci., Publ. Math. , mrclass =. 1966 , bdsk-url-1 =
work page 1966
-
[12]
Springer, T. A. , date-added =. Linear. 2009 , bdsk-url-1 =
work page 2009
-
[13]
Group theoretical characterizations of rationality , volume =
Regeta, Andriy and Urech, Christian and van Santen, Immanuel , date-added =. Group theoretical characterizations of rationality , volume =. Invent. Math. , keywords =. 2025 , zbmath =. doi:10.1007/s00222-025-01348-7 , fjournal =
-
[14]
On the triviality of a family of linear hyperplanes , volume =
Ghosh, Parnashree and Gupta, Neena , fjournal =. On the triviality of a family of linear hyperplanes , volume =. Adv. Math. , pages =. 2023 , bdsk-url-1 =
work page 2023
-
[15]
Gupta, Neena , date-modified =. On. Adv. Math. , pages =. 2014 , bdsk-url-1 =
work page 2014
-
[16]
Representations of algebraic groups , volume =
Jantzen, Jens Carsten , date-added =. Representations of algebraic groups , volume =
-
[17]
Additive group actions on affine
Langlois, Kevin and Liendo, Alvaro , date-added =. Additive group actions on affine. J. Algebra , mrclass =. 2016 , bdsk-url-1 =. doi:10.1016/j.jalgebra.2015.11.019 , fjournal =
-
[18]
On the topologies on ind-varieties and related irreducibility questions , url =
Stampfli, Immanuel , date-added =. On the topologies on ind-varieties and related irreducibility questions , url =. J. Algebra , mrclass =. 2012 , bdsk-url-1 =. doi:10.1016/j.jalgebra.2012.08.019 , fjournal =
-
[19]
Popov, Vladimir L. , date-added =. Group varieties and group structures , url =. Izv. Ross. Akad. Nauk Ser. Mat. , mrclass =. 2022 , bdsk-url-1 =. doi:10.4213/im9272 , fjournal =
-
[20]
van der Kulk, W. , date-added =. On polynomial rings in two variables , volume =. Nieuw Arch. Wisk. (3) , mrclass =
-
[21]
Gutwirth, A. , date-added =. The action of an algebraic torus on the affine plane , url =. Trans. Amer. Math. Soc. , mrclass =. 1962 , bdsk-url-1 =. doi:10.2307/1993728 , fjournal =
-
[22]
Miyanishi, Masayoshi , date-added =. Nagoya Math. J. , mrclass =. 1971 , bdsk-url-1 =
work page 1971
-
[23]
Pseudo-reductive groups , url =
Conrad, Brian and Gabber, Ofer and Prasad, Gopal , date-added =. Pseudo-reductive groups , url =. 2010 , bdsk-url-1 =. doi:10.1017/CBO9780511661143 , isbn =
-
[24]
Approximation theory and the rank of abelian varieties over large algebraic fields , url =
Frey, Gerhard and Jarden, Moshe , date-added =. Approximation theory and the rank of abelian varieties over large algebraic fields , url =. Proc. London Math. Soc. (3) , mrclass =. 1974 , bdsk-url-1 =. doi:10.1112/plms/s3-28.1.112 , fjournal =
-
[25]
Mumford, David , date-added =. Abelian
-
[26]
On fixed point schemes of actions of multiplicative and additive groups , url =
Bia. On fixed point schemes of actions of multiplicative and additive groups , url =. Topology , mrclass =. 1973 , bdsk-url-1 =. doi:10.1016/0040-9383(73)90024-4 , fjournal =
-
[27]
Bass, Hyman and Connell, Edvin H. and Wright, David L. , date-added =. Locally polynomial algebras are symmetric algebras , url =. Invent. Math. , mrclass =. 1976/77 , bdsk-url-1 =. doi:10.1007/BF01403135 , fjournal =
-
[28]
Bardsley, Peter and Richardson, R. W. , date-added =. \'Etale slices for algebraic transformation groups in characteristic. Proc. London Math. Soc. (3) , mrclass =. 1985 , bdsk-url-1 =. doi:10.1112/plms/s3-51.2.295 , fjournal =
-
[29]
Automorphism groups of affine varieties consisting of algebraic elements , url =
Perepechko, Alexander and Regeta, Andriy , doi =. Automorphism groups of affine varieties consisting of algebraic elements , url =. Proc. Amer. Math. Soc. , number =. 2024 , bdsk-url-1 =
work page 2024
-
[30]
Sous-groupes alg\'ebriques de rang maximum du groupe de
Demazure, Michel , date-added =. Sous-groupes alg\'ebriques de rang maximum du groupe de. Ann. Sci. \'Ecole Norm. Sup. (4) , mrclass =. 1970 , bdsk-url-1 =
work page 1970
-
[31]
Op\'erations du groupe additif sur le plan affine , volume =
Rentschler, Rudolf , date-added =. Op\'erations du groupe additif sur le plan affine , volume =. C. R. Acad. Sci. Paris S\'er. A-B , mrclass =
-
[32]
Bass, Hyman , date-added =. A nontriangular action of. J. Pure Appl. Algebra , mrclass =. 1984 , bdsk-url-1 =. doi:10.1016/0022-4049(84)90019-7 , fjournal =
-
[33]
Dynamical properties of plane polynomial automorphisms , url =
Friedland, Shmuel and Milnor, John , doi =. Dynamical properties of plane polynomial automorphisms , url =. Ergodic Theory Dynam. Systems , mrclass =. 1989 , bdsk-url-1 =
work page 1989
-
[34]
On the maximality of the triangular subgroup , url =
Furter, Jean-Philippe and Poloni, Pierre-Marie , date-added =. On the maximality of the triangular subgroup , url =. Ann. Inst. Fourier (Grenoble) , mrclass =. 2018 , bdsk-url-1 =. doi:10.5802/aif.3165 , fjournal =
-
[35]
Liendo, Alvaro , date-added =. Affine. Transform. Groups , mrclass =. 2010 , bdsk-url-1 =. doi:10.1007/s00031-010-9089-2 , fjournal =
-
[36]
Contributions to the Essential Dimension of Finite and Algebraic Groups , url =
Loetscher, Roland , date-added =. Contributions to the Essential Dimension of Finite and Algebraic Groups , url =. 2010 , bdsk-url-1 =
work page 2010
-
[37]
Suprunenko, D. A. , date-added =. Matrix
- [38]
- [39]
-
[40]
Characterizing smooth affine spherical varieties via the automorphism group , url =
Regeta, Andriy and van Santen, Immanuel , date-added =. Characterizing smooth affine spherical varieties via the automorphism group , url =. J. \'Ec. polytech. Math. , mrclass =. 2021 , bdsk-url-1 =. doi:10.5802/jep.149 , fjournal =
-
[41]
Berest, Yuri and Eshmatov, Alimjon and Eshmatov, Farkhod , doi =. Dixmier groups and. Adv. Math. , mrclass =. 2016 , bdsk-url-1 =
work page 2016
-
[42]
Remarks on the action of an algebraic torus on
Bia. Remarks on the action of an algebraic torus on. Bull. Acad. Polon. Sci. S\'er. Sci. Math. Astronom. Phys. , mrclass =
-
[43]
Linear algebraic groups , url =
Borel, Armand , doi =. Linear algebraic groups , url =. 1991 , bdsk-url-1 =
work page 1991
-
[44]
Homogeneous varieties under split solvable algebraic groups , url =
Brion, Michel , doi =. Homogeneous varieties under split solvable algebraic groups , url =. Indag. Math. (N.S.) , mrclass =. 2021 , bdsk-url-1 =
work page 2021
- [45]
-
[46]
Families of commuting automorphisms, and a characterization of the affine space , url =
Cantat, Serge and Regeta, Andriy and Xie, Junyi , doi =. Families of commuting automorphisms, and a characterization of the affine space , url =. Amer. J. Math. , mrclass =. 2023 , bdsk-url-1 =
work page 2023
-
[47]
Cantat, Serge and Kraft, Hanspeter and Regeta, Andriy and van Santen, Immanuel , date-modified =. On. preprint , pages =. 2025 , bdsk-url-1 =
work page 2025
-
[48]
Demazure, Michel and Gabriel, Pierre , mrclass =. Groupes alg\'ebriques
-
[49]
Computing invariants of algebraic groups in arbitrary characteristic , url =
Derksen, Harm and Kemper, Gregor , doi =. Computing invariants of algebraic groups in arbitrary characteristic , url =. Adv. Math. , mrclass =. 2008 , bdsk-url-1 =
work page 2008
-
[50]
Epstein, D. B. A. and Thurston, W. P. , doi =. Transformation groups and natural bundles , url =. Proc. London Math. Soc. (3) , mrclass =. 1979 , bdsk-url-1 =
work page 1979
-
[51]
Actions and invariants of algebraic groups , url =
Ferrer Santos, Walter Ricardo and Rittatore, Alvaro , doi =. Actions and invariants of algebraic groups , url =. 2017 , bdsk-url-1 =
work page 2017
-
[52]
G\"ortz, Ulrich and Wedhorn, Torsten , doi =. Algebraic geometry. [2020] 2020 , bdsk-url-1 =
work page 2020
-
[53]
G\"ortz, Ulrich and Wedhorn, Torsten , date-added =. Algebraic geometry. doi:https://doi.org/10.1007/978-3-658-43031-3 , edition =
-
[54]
Geometric quotients of unipotent group actions , url =
Greuel, Gert-Martin and Pfister, Gerhard , doi =. Geometric quotients of unipotent group actions , url =. Proc. London Math. Soc. (3) , mrclass =. 1993 , bdsk-url-1 =
work page 1993
-
[55]
Grothendieck, Alexander , date-modified =. Inst. Hautes \'Etudes Sci. Publ. Math. , mrclass =. 1961 , bdsk-url-1 =
work page 1961
-
[56]
Grothendieck, Alexander , date-modified =. Inst. Hautes \'Etudes Sci., Publ. Math. , mrclass =. 1965 , bdsk-url-1 =
work page 1965
-
[57]
Gubeladze, I. Dzh. , fjournal =. The. Soobshch. Akad. Nauk Gruzin. SSR , mrclass =
-
[58]
Hochster, Melvin and Roberts, Joel L. , doi =. Rings of invariants of reductive groups acting on regular rings are. Advances in Math. , mrclass =. 1974 , bdsk-url-1 =
work page 1974
-
[59]
A complement of a hypersurface in affine variety , volume =
Jelonek, Zbigniew , fjournal =. A complement of a hypersurface in affine variety , volume =. Bull. Polish Acad. Sci. Math. , mrclass =
-
[60]
The set of fixed points of a unipotent group , volume =
Jelonek, Zbigniew and Laso. The set of fixed points of a unipotent group , volume =. J. of Algebra , number =
-
[61]
Jung, Heinrich W. E. , date-modified =. J. Reine Angew. Math. , mrclass =. 1942 , bdsk-url-1 =. doi:10.1515/crll.1942.184.161 , fjournal =
-
[62]
On automorphism groups of affine surfaces , url =
Kovalenko, Sergei and Perepechko, Alexander and Zaidenberg, Mikhail , booktitle =. On automorphism groups of affine surfaces , url =. 2017 , bdsk-url-1 =. doi:10.2969/aspm/07510207 , isbn =
- [63]
-
[64]
Is the affine space determined by its automorphism group? , url =
Kraft, Hanspeter and Regeta, Andriy and van Santen, Immanuel , date-modified =. Is the affine space determined by its automorphism group? , url =. Int. Math. Res. Not. IMRN , mrclass =. 2021 , bdsk-url-1 =. doi:10.1093/imrn/rny281 , fjournal =
-
[65]
Algebraically generated groups and their
Kraft, Hanspeter and Zaidenberg, Mikhail , doi =. Algebraically generated groups and their. J. Lond. Math. Soc. (2) , mrclass =. 2024 , bdsk-url-1 =
work page 2024
-
[66]
Lamy, St\'ephane , date-modified =. L'alternative de. J. Algebra , mrclass =. 2001 , bdsk-url-1 =. doi:10.1006/jabr.2000.8701 , fjournal =
-
[67]
Lamy, St\'ephane , date-modified =. The. 2025 , bdsk-url-1 =
work page 2025
- [68]
-
[69]
Luna, Domingo , booktitle =. Slices \'etales , url =. 1973 , bdsk-url-1 =. doi:10.24033/msmf.110 , mrclass =
-
[70]
Makedonskyi, Ie. O. and Petravchuk, A. P. , doi =. On nilpotent and solvable. J. Algebra , mrclass =. 2014 , bdsk-url-1 =
work page 2014
- [71]
-
[72]
Mostow, G. D. , doi =. Fully reducible subgroups of algebraic groups , url =. Amer. J. Math. , mrclass =. 1956 , bdsk-url-1 =
work page 1956
-
[73]
Mumford, David , date-modified =. The. 1999 , bdsk-url-1 =. doi:10.1007/b62130 , edition =
-
[74]
Nagata, Masayoshi , booktitle =. On the fourteenth problem of
-
[75]
Lectures on the fourteenth problem of
Nagata, Masayoshi , date-modified =. Lectures on the fourteenth problem of
-
[76]
Neeman, Amnon , doi =. Steins, affines and. Ann. of Math. (2) , mrclass =. 1988 , bdsk-url-1 =
work page 1988
-
[77]
Structure of connected nested automorphism groups , volume =
Perepechko, Alexander , journal =. Structure of connected nested automorphism groups , volume =
-
[78]
Perrin, Daniel , date-modified =. Algebraic. 2008 , bdsk-url-1 =. doi:10.1007/978-1-84800-056-8 , isbn =
-
[79]
Popov, Vladimir L. , doi =. On infinite dimensional algebraic transformation groups , url =. Transform. Groups , mrclass =. 2014 , bdsk-url-1 =
work page 2014
-
[80]
Ramanujam, C. P. , doi =. A note on automorphism groups of algebraic varieties , url =. Math. Ann. , mrclass =. 1964 , bdsk-url-1 =
work page 1964
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