Coherent sheaves on subvarieties in Hopf manifolds
Pith reviewed 2026-06-27 23:36 UTC · model grok-4.3
The pith
Normal varieties with holomorphic contractions acquire affine structure and their quotients in Hopf manifolds have filtrable reflexive sheaves.
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
Core claim
A normal complex analytic variety X equipped with an invertible holomorphic contraction γ centered at x admits a natural affine algebraic structure. Any γ-equivariant reflexive coherent sheaf on X is algebraic. The punctured space X0 = X ackslash x carries a proper C* action and is the total space of a non-zero section of an ample line bundle over the projective orbifold Z = X0/C*. The quotient M = X0/γ embeds holomorphically into a Hopf manifold, and conversely every normal subvariety of a Hopf manifold is obtained this way. Any reflexive coherent sheaf on M with dim M > 2 admits a filtration such that the associated graded subquotients, after tensoring with an appropriate line bundle, ari
What carries the argument
The invertible holomorphic contraction γ, which equips X with affine structure, induces the C* action on X0, produces the projective quotient Z, and yields the embedding of M into a Hopf manifold.
If this is right
- X acquires the structure of an affine algebraic variety.
- Every γ-equivariant reflexive coherent sheaf on X becomes an algebraic sheaf.
- M = X0/γ embeds holomorphically into a Hopf manifold, and the converse holds for all normal subvarieties of Hopf manifolds.
- Reflexive coherent sheaves on M with dim M > 2 admit a filtration whose graded pieces are pullbacks from Z after twisting by a line bundle.
- Every reflexive coherent sheaf on such an M is filtrable, with all successive quotients of rank at most one.
Where Pith is reading between the lines
- The correspondence between M and the pair (Z, line bundle) suggests that many analytic invariants of sheaves on M can be read off from the projective geometry of Z.
- The dimension restriction dim M > 2 may mark the threshold where filtrability fails in lower dimensions or for non-normal varieties.
- The same contraction data could be used to compare deformation spaces of M with those of the projective orbifold Z.
Load-bearing premise
The normal complex analytic variety X must admit an invertible holomorphic contraction centered at a single point.
What would settle it
A normal subvariety M of dimension greater than 2 inside a Hopf manifold together with a reflexive coherent sheaf on M that admits no filtration whose successive quotients all have rank at most one would falsify the structure theorem.
read the original abstract
We prove a version of GAGA theorem for a normal complex analytic variety $X$ equipped with an invertible holomorphic contraction $\gamma$ with center in $x$. We show that $X$ admits a natural structure of an affine variety, and any $\gamma$-equivariant complex analytic reflexive coherent sheaf on $X$ admits a natural algebraic structure. We prove a structure theorem for $X_0:=X\backslash x$, showing that it admits a proper action of ${\Bbb C}^*$, and is isomorphic to the space of non-zero vectors in the total space of an ample line bundle over the projective variety $Z:= X_0/{\mathbb C}^*$ equipped with an orbifold structure. We show that the quotient $M:=X_0/\gamma$ admits a holomorphic embedding to a Hopf manifold, and, conversely, any normal subvariety $M$ in a Hopf manifold is obtained this way. We prove a form of structure theorem, showing that any reflexive coherent sheaf on $M$, $\dim M > 2$, admits a filtration such that its associated graded subquotients, tensored with an appropriate line bundle, are obtained as pullbacks of coherent sheaves on the projective variety $Z=X_0/{\mathbb C}^*$. This is used to show that any reflexive coherent sheaf on $M$ is filtrable, that is, admits a filtration with associated graded quotients of rank $\leq 1$.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper proves a GAGA-type theorem for a normal complex analytic variety X equipped with an invertible holomorphic contraction γ centered at a point x. It shows that X admits a natural affine algebraic structure, that γ-equivariant reflexive coherent sheaves on X are algebraic, that X0 = X ackslash {x} carries a proper C* action making it the total space of an ample line bundle over the projective orbifold Z = X0/C*, that the quotient M = X0/γ embeds holomorphically into a Hopf manifold (with the converse holding for normal subvarieties), and that for dim M > 2 any reflexive coherent sheaf on M admits a filtration whose associated graded pieces, after tensoring with a suitable line bundle, are pullbacks of coherent sheaves from Z; this implies every such sheaf is filtrable with rank-≤1 graded quotients.
Significance. If the results hold, the work supplies an algebraic structure on certain non-projective analytic varieties via contractions and gives a concrete filtrability theorem for reflexive sheaves on subvarieties of Hopf manifolds. The characterization of such subvarieties via C*-quotients and the reduction of sheaf filtrations to pullbacks from the projective orbifold Z are potentially useful extensions of GAGA principles beyond the projective case. The manuscript ships a self-contained logical chain from the contraction hypothesis through the orbifold quotient to the filtrability statement.
minor comments (2)
- The abstract states that M embeds into a Hopf manifold and conversely, but the precise statement of the embedding theorem (including any dimension or normality hypotheses) should be cross-referenced to the corresponding theorem number in the body for clarity.
- Notation for the orbifold structure on Z = X0/C* is introduced without an explicit local chart description; a brief sentence recalling the standard definition of orbifold quotient would aid readers unfamiliar with the construction.
Simulated Author's Rebuttal
We thank the referee for their positive summary of the manuscript and for recommending acceptance. We are pleased that the logical chain from the contraction hypothesis to the filtrability statement was found clear and self-contained.
Circularity Check
No significant circularity detected
full rationale
The derivation begins from the explicit hypothesis that X admits an invertible holomorphic contraction γ with center at x, then constructs the affine algebraic structure on X, the C* action on X0, the projective quotient Z, the embedding of M into a Hopf manifold, and the filtration on reflexive sheaves whose graded pieces are pullbacks from Z. Each step is presented as a direct consequence of the contraction assumption and standard properties of normal varieties and coherent sheaves (with the dim M > 2 condition serving only to guarantee filtrability). No equation or claim reduces by definition to its own input, no parameter is fitted and then relabeled as a prediction, and no load-bearing premise is justified solely by a self-citation whose content is unverified. The argument is therefore self-contained within the stated hypotheses.
Axiom & Free-Parameter Ledger
axioms (1)
- standard math Standard theorems and definitions from complex analytic geometry and algebraic geometry (including classical GAGA and properties of Hopf manifolds) hold.
Reference graph
Works this paper leans on
-
[1]
Abramovich, and B
D. Abramovich, and B. Hassett, Stable varieties with a twist, in Classification of Algebraic Varieties 3 , 1-38, EMS Ser. Congr. Rep., EMS, Z\"urich, 2011
2011
-
[2]
Andreotti, R
A. Andreotti, R. Narasimhan, Oka's Heftungslemma and the Levi Problem for Complex Spaces , Trans. Amer. Math. Soc. 111 (1964), 346-366
1964
-
[3]
Andreotti, Y
A. Andreotti, Y. T. Siu, Projective embeddings of pseudoconcave spaces , Ann. Scuola Norm. Sup. Pisa 24 , 231-278 (1970)
1970
-
[4]
Aprodu, M
M. Aprodu, M. Toma, Une note sur les fibr'es holomorphes non-filtrables , C. R. Math. Acad. Sci. Paris 336 (2003), no. 7, 581-584
2003
-
[5]
V. I. Arnol'd, Geometrical Methods in the Theory of Ordinary Differential Equations, Grundlehren der mathematischen Wissenschaften 250 , Springer, 1996
1996
-
[6]
Artin, Algebraic approximation of structures over complete local rings, Publ
M. Artin, Algebraic approximation of structures over complete local rings, Publ. Math. IH\'ES, 36 (36) (1969). 23-58
1969
-
[7]
M. F. Atiyah, I. G. MacDonald, Introduction to commutative algebra, Addison-Wesley, 1969
1969
-
[8]
Baily, The decomposition theorem for V-manifolds , Amer
W.L. Baily, The decomposition theorem for V-manifolds , Amer. J. Math. 78 (1956), 862-888. 32.00 (31.00)
1956
-
[9]
Baily, On the imbedding of V-manifolds in projective spaces, Amer
W.L. Baily, On the imbedding of V-manifolds in projective spaces, Amer. J. Math. 79 (1957), 403-430
1957
-
[10]
B anic a, J
C. B anic a, J. Le Potier Sur l'existence des fibr\'es vectoriels holomorphes sur les surfaces non-alg\'ebriques , J. Reine Angew. Math. 378 (1987), 1-31
1987
-
[11]
Springer Verlag, Berlin-Heidelberg, 2004
Barth, W., Hulek, K., Peters, C., van de Ven, A., Compact complex surfaces, Second enlarged edition. Springer Verlag, Berlin-Heidelberg, 2004
2004
-
[12]
atsbereichen und die Meromorphiekonvexit\
H. Behnke, K. Stein, Konvergente Folgen Von Regularit\"atsbereichen und die Meromorphiekonvexit\"at , Math. Ann. 116 (1939) 204-216
1939
-
[13]
Berteloot, M\'ethodes de changement d'\'echelles en analyse complexe , Ann
F. Berteloot, M\'ethodes de changement d'\'echelles en analyse complexe , Ann. Fac. Sci. Toulouse Math., Tome XV , 3 (2006), p.427-483
2006
-
[14]
Borel, Linear algebraic groups , GTM 176 , Springer-Verlag, 1991
A. Borel, Linear algebraic groups , GTM 176 , Springer-Verlag, 1991
1991
-
[15]
Borel, J
A. Borel, J. Tits, Groupes r\'eductives , Publications Math\'ematiques de l'IH\'ES, 27 (1965), 55-151
1965
-
[16]
C. P. Boyer, K. Galicki, Sasakian geometry , Oxford Univ. Press, Oxford, 2008
2008
-
[17]
Boureau, Normal forms and geometric structures on Hopf manifolds , arXiv:2501.10346
P. Boureau, Normal forms and geometric structures on Hopf manifolds , arXiv:2501.10346
-
[18]
Br\^inz a nescu Holomorphic Vector Bundles over Compact Complex Surfaces , LNM 1624 , Springer Verlag, 1996
V. Br\^inz a nescu Holomorphic Vector Bundles over Compact Complex Surfaces , LNM 1624 , Springer Verlag, 1996
1996
-
[19]
Br\^inz anescu, R
V. Br\^inz anescu, R. Moraru Holomorphic rank-2 vector bundles on non-K"ahler elliptic surfaces, Ann. Inst. Fourier 55 No. 5 (2005), 1659-1683
2005
-
[20]
M. E. Calle, Orbispaces as stacks: geometry and examples, talk notes , https://hiroleetanaka.com/workshop-2025/notes-05.pdf
2025
-
[21]
Cantat, R
S. Cantat, R. Dujardin, Holomorphically conjugate polynomial automorphisms of C ^2 are polynomially conjugate, Bull. London Math. Soc., 56 (2024), 3745-3751
2024
-
[22]
A. Clarke, C. Tipler, Blowing-up hermitian Yang-Mills connections, Ann. Scuola Norm. Sup. Pisa Cl. Sci., 23 . https://doi.org/10.2422/2036-2145.202311_009
-
[23]
C. H. Clemens, Degeneration of K\"ahler manifolds , Duke Math. J. 44 (1977), no. 2, 215-290
1977
-
[24]
Deligne, Cat\'egories tannakiennes , The Grothendieck Festschrift, Vol
P. Deligne, Cat\'egories tannakiennes , The Grothendieck Festschrift, Vol. II, Progr. Math. 87 , Birkh\"auser Boston, Boston, MA, 1990, 111-195
1990
-
[25]
Demailly, Complex analytic and differential geometry , https://www-fourier.ujf-grenoble.fr/ demailly/manuscripts/agbook.pdf
J.-P. Demailly, Complex analytic and differential geometry , https://www-fourier.ujf-grenoble.fr/ demailly/manuscripts/agbook.pdf
-
[26]
Dloussky, Structure des surfaces de Kato, M\'em
G. Dloussky, Structure des surfaces de Kato, M\'em. Soc. Math. France (N.S.) No. 14 (1984)
1984
-
[27]
Dulac, Solutions d'un syst\`eme d'\'equations diff\'erentielles dans le voisinage des valeurs singuli\`eres, Bull
H. Dulac, Solutions d'un syst\`eme d'\'equations diff\'erentielles dans le voisinage des valeurs singuli\`eres, Bull. Soc. Math. France, 40 (1912), 324-383
1912
-
[28]
Elencwajg and O
G. Elencwajg and O. Forster, Vector bundles on manifolds without divisors and a theorem on deformations, Ann. Inst. Fourier 32.4 (1982), 25-51
1982
-
[29]
Favre, M
C. Favre, M. Ruggiero, Normal surface singularities admitting contracting automorphisms , Ann. Fac. Sci. Toulouse Math. 23 (2014), 797--828
2014
-
[30]
Forster, Zur Theorie der Steinschen Algebren und Moduln , Math
O. Forster, Zur Theorie der Steinschen Algebren und Moduln , Math. Z., 97:376-405, 1967
1967
-
[31]
Friedland, J
S. Friedland, J. Milnor, Dynamical properties of plane polynomial automorphisms, Ergodic Theory Dynam. Systems 9 (1) (1989), 67-99
1989
-
[32]
Friedman, Foundations of modern analysis , Dover, 2010
A. Friedman, Foundations of modern analysis , Dover, 2010
2010
-
[33]
Gauduchon, L
P. Gauduchon, L. Ornea, Locally conformally K\"ahler metrics on Hopf surfaces , Ann. Inst. Fourier (Grenoble) 48 (1998), 1107-1128
1998
-
[34]
Grothendieck, Th\'eor\`emes de finitude pour la cohomologie des faisceaux , Bull
A. Grothendieck, Th\'eor\`emes de finitude pour la cohomologie des faisceaux , Bull. S. M. F., tome 84 (1956), 1-7
1956
-
[35]
Grothendieck, \'El\'ements de g\'eom\'etrie alg\'ebrique: IV
A. Grothendieck, \'El\'ements de g\'eom\'etrie alg\'ebrique: IV. \'Etude locale des sch\'emas et des morphismes de sch\'emas, Seconde partie, Publ. Math. Inst. Hautes Études Sci. 24 (1965), 5-231
1965
-
[36]
Grothendieck, SGA 3, Exp
A. Grothendieck, SGA 3, Exp. I, in Demazure-Grothendieck (eds.), Sch\'emas en groupes I, LNM 151 , Springer, 1970
1970
-
[37]
R. C. Gunning, H. Rossi, Analytic functions of several complex variables , Reprint of the 1965 original. AMS Chelsea Publishing, Providence, RI, 2009
1965
-
[38]
Hartshorne, Stable reflexive sheaves , Math
R. Hartshorne, Stable reflexive sheaves , Math. Ann. 254, 121-176 (1980)
1980
-
[39]
J. E. Humphreys, Linear algebraic groups , GTM 21, 4th ed., Springer, 1998
1998
-
[40]
ahler manifolds . alg-geom 9712012, a chapter in a book ``Hyperk\
D. Kaledin, M. Verbitsky. Hyperholomorphic sheaves and new examples of hyperk\"ahler manifolds . alg-geom 9712012, a chapter in a book ``Hyperk\"ahler manifolds'' International Press, Boston, 2001
2001
-
[41]
Kato, Some Remarks on Subvarieties of Hopf Manifolds, Tokyo J
Ma. Kato, Some Remarks on Subvarieties of Hopf Manifolds, Tokyo J. Math. 2 , Nr. 1 (1979), 47--61
1979
-
[42]
L. Kaup, B. Kaup, Holomorphic Functions of Several Complex Variables , de Gruyter, 1983
1983
-
[43]
Kodaira, On the structure of compact complex surfaces, III , Amer
K. Kodaira, On the structure of compact complex surfaces, III , Amer. J. Math. 90 (1968), 55-83
1968
-
[44]
Koll\'ar, Quotient Spaces Modulo Algebraic Groups , Annals of Math
J. Koll\'ar, Quotient Spaces Modulo Algebraic Groups , Annals of Math. 145 , No. 1 (1997), 33-79
1997
-
[45]
Korshunov, ``Polynomial contractions acting as automorphisms of C ^n '', MathOverflow, 2026
D. Korshunov, ``Polynomial contractions acting as automorphisms of C ^n '', MathOverflow, 2026. https://mathoverflow.net/questions/507828/polynomial-contractions-acting-as-automorphisms-of-bbb-cn
2026
-
[46]
Korshunov, Polynomial contractions, degree growth, and exotic algebraic ^n , arXiv:2605.29386
D. Korshunov, Polynomial contractions, degree growth, and exotic algebraic ^n , arXiv:2605.29386
-
[47]
Haefliger, Some rem
A. Haefliger, Some rem
-
[48]
Kamishima, L
Y. Kamishima, L. Ornea,
-
[49]
L\"ubke, A
M. L\"ubke, A. Teleman, The Kobayashi-Hitchin correspondence , World Scientific Publishing Co., Inc., River Edge, NJ, 1995. x+254 pp
1995
-
[50]
Molino, Riemannian foliations , Birkh\"auser, 1988
P. Molino, Riemannian foliations , Birkh\"auser, 1988
1988
-
[51]
Lerman, Orbifolds as stacks? L'Enseign
E. Lerman, Orbifolds as stacks? L'Enseign. Math. (2) 56 (2010), no. 3-4, 315--363
2010
-
[52]
Madera, Holomorphic geometric structures on Hopf manifolds , arXiv:2501.11364
M. Madera, Holomorphic geometric structures on Hopf manifolds , arXiv:2501.11364
-
[53]
J. S. Milne, Algebraic Groups. The theory of group schemes of finite type over a field , Cambridge University Press; 2017. Also: https://www.jmilne.org/math/Books/iAG2022.pdf
2017
-
[54]
Moerdijk, D
I. Moerdijk, D. A. Pronk, Orbifolds, sheaves and groupoids , K-Theory, 12 (1) (1997), 3-21
1997
-
[55]
Morvan, Singularities Admitting Contracting Automorphisms , arXiv:2412.11583
K. Morvan, Singularities Admitting Contracting Automorphisms , arXiv:2412.11583
-
[56]
Okonek, M
C. Okonek, M. Schneider, H. Spindler, Vector bundles on complex projective spaces. Progress in math., vol. 3 , Birkhauser, 1980
1980
-
[57]
Orlik, P
P. Orlik, P. Wagreich, Isolated Singularities of Algebraic Surfaces with ^* -Action Annals of Math. 93 , No. 2 (1971), 205-228
1971
-
[58]
Ornea, A
L. Ornea, A. Otiman, M. Stanciu, Compatibility between non-K\" ahler structures on complex (nil)manifolds , Transf. Groups 28 (2023), 1669-1686
2023
-
[59]
Ornea, M
L. Ornea, M. Verbitsky, Locally conformal K\"ahler manifolds with potential , Math. Ann. 348 (2010), 25-33
2010
-
[60]
Ornea, M
L. Ornea, M. Verbitsky, Locally conformally K\"ahler metrics obtained from pseudoconvex shells , Proc. Amer. Math. Soc. 144 (2016), 325-335
2016
-
[61]
Ornea, M
L. Ornea, M. Verbitsky,
-
[62]
Ornea, M
L. Ornea, M. Verbitsky, Embedding of LCK manifolds with potential into Hopf manifolds using Riesz--Schauder theorem , ``Complex and Symplectic Geometry'', Springer INdAM series, 2017, 137-148
2017
-
[63]
Ornea, M
L. Ornea, M. Verbitsky, Hopf surfaces in locally conformally K\"ahler manifolds with potential , Geom. Dedicata 207 (2020), 219-226
2020
- [64]
-
[65]
ahler geometry , Progress in Math. 354 , Birkh\
L. Ornea, M. Verbitsky, Principles of locally conformally K\"ahler geometry , Progress in Math. 354 , Birkh\"auser, 2024, arXiv:2208.07188
arXiv 2024
- [66]
-
[67]
Ornea, M
L. Ornea, M. Verbitsky, Mall bundles and flat connections , Ann. Inst. Fourier (Grenoble) 75 (2025), no. 1, 331-358
2025
-
[68]
Persson, On degenerations of algebraic surfaces , Mem
U. Persson, On degenerations of algebraic surfaces , Mem. Amer. Math. Soc. 11 (1977), no. 189
1977
-
[69]
Poincar\'e, Sur les propri\'et\'es des fonctions d\'efinies par les \'equations aux diff\'erences partielles, Paris, Gauthier-Villars, 1879
H. Poincar\'e, Sur les propri\'et\'es des fonctions d\'efinies par les \'equations aux diff\'erences partielles, Paris, Gauthier-Villars, 1879
-
[70]
Rummler, Quelques notions si
H. Rummler, Quelques notions si
-
[71]
Ornea, M
L. Ornea, M. Verbitsky, Bimeromorphic geometry of LCK manifolds ,
-
[72]
Ornea, M
L. Ornea, M. Verbitsky, V. Vuletescu, Blow-ups of locally conformally K\"ahler manifolds , Int. Math. Res. Not. IMRN 2013, no. 12, 2809-2821
2013
-
[73]
Otiman, Morse--Novikov cohomology of locally conformally K\"ahler surfaces , Math
A. Otiman, Morse--Novikov cohomology of locally conformally K\"ahler surfaces , Math. Z. 289 (2018), no. 1-2, 605-628. arXiv:1609.07675
Pith/arXiv arXiv 2018
-
[74]
Preda, M
O. Preda, M. Stanciu, Coverings of locally conformally K\"ahler complex spaces , Math. Z. 298 (2021), 639-651
2021
-
[75]
Preda, M
O. Preda, M. Stanciu, Vaisman theorem for lcK spaces , Ann. Scuola Norm. Sup. Pisa, Vol. XXIV (2023), 2311-2321
2023
-
[76]
Roberts, A note on coherent G-sheaves, Math
M. Roberts, A note on coherent G-sheaves, Math. Ann. 275 (1986), 573-582
1986
-
[77]
J. Ross, R. Thomas, Weighted projective embeddings, stability of orbifolds, and constant scalar curvature K\"ahler metrics , J. Differential Geom. 88 (2011), no. 1, 109-159
2011
-
[78]
aten von Hyperfl\
K. Saito, Quasihomogene isolierte Singularit\"aten von Hyperfl\"achen, Invent. Math. 14 (1971), 123-142
1971
-
[79]
Serre, Faisceaux alg\'ebriques coh\'erents , Annals of Math., 61 (2) (1955) 197-278
J.-P. Serre, Faisceaux alg\'ebriques coh\'erents , Annals of Math., 61 (2) (1955) 197-278
1955
-
[80]
Serre, G\'eom\'etrie alg\'ebrique et g\'eom\'etrie analytique , Ann.Inst
J.-P. Serre, G\'eom\'etrie alg\'ebrique et g\'eom\'etrie analytique , Ann.Inst. Fourier 6 (1956), 1-42
1956
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