REVIEW 3 major objections 3 minor 42 references
Kummers, spinors, and heights
T0 review · 3 major / 3 minor · reviewed 2026-08-06 · deepseek-v4-flash
Pith's one-line read The paper gives an explicit pure-spinor description of the Kummer embedding for every odd hyperelliptic Jacobian, and uses it to prove a density-one lower bound for canonical heights.
desk verdict The explicit Kummer embedding for all g is a solid, citeable contribution; the density-one canonical-height theorem is not proved as stated. read the letter →
The pith
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
The reading
What carries the argument
The load-bearing object is the morphism $\Psi\colon J_f\to OGr(g,V)$, where $V=k[x]/(f(x))$ carries the bilinear form $\psi(a,b)=\tau(ab)$ and $OGr(g,V)$ is the orthogonal Grassmannian of isotropic $g$-planes. Its composition with the spinor embedding realizes the complete linear system $|2\Theta|$: points of the Kummer variety correspond to pure spinors, i.e. lines in the spin representation $S$ whose annihilator is a maximal isotropic subspace, and the coordinates are Pfaffians in the coefficients of the Mumford triple. The Clifford group of $V$ supplies matrices for the $\theta$ group $G(2\Theta)$, and the duplication map $[2]$ is represented by explicit quartic polynomials; this linear-algebraic package is what allows the naive, reduction, and canonical heights to be compared uniformly in $g$.
What would settle it
For a positive-density sequence of polynomials $f(x)=x^{2g+1}+c_2x^{2g-1}+\cdots+c_{2g+1}\in\mathbb{Z}[x]$ with $Ht(f)\to\infty$, construct a rational point $P\in J_f(\mathbb{Q})$ given by a Mumford triple and evaluate the paper's duplication polynomials to compute $\widehat{h}_\Theta(P)$; if such points have $\widehat{h}_\Theta(P)<((3g-1)/2-\epsilon)\log Ht(f)$ infinitely often, the density-one theorem is false.
Extended reading notes
Core claim
The central discovery is that the $|2\Theta|$ linear system of an odd hyperelliptic Jacobian is governed by the same quadratic space $V=k[x]/(f(x))$ that carries the Mumford representation: the Kummer embedding $K_f\to\mathbb{P}^{2^g-1}$ is the composite of a morphism $\Psi\colon J_f\to OGr(g,V)$ with the pure-spinor embedding $\Sigma\colon OGr(g,V)\to\mathbb{P}(S)$, and both factors are computable from the triple $(U,V,R)$. Clifford multiplication gives the $\theta$-group action on $H^0(J_f,\mathcal{O}_{J_f}(2\Theta))$, explicit matrices for lifts of $2$-torsion points, and quartic polynomials representing duplication. The main arithmetic consequence is Theorem 1.4: for fixed $g\ge1$ and $\epsilon>0$, $100\%$ of polynomials $f(x)=x^{2g+1}+c_2x^{2g-1}+\cdots+c_{2g+1}\in\mathbb{Z}[x]$ of nonzero discriminant satisfy $\widehat{h}_\Theta(P)\ge((3g-1)/2-\epsilon)\log Ht(f)$ for every non-trivial $P\in J_f(\mathbb{Q})$; the body proves this for the $c_1=0$ family, and the abstract's all-monic statement is asserted rather than proved.
Load-bearing premise
The load-bearing premise is an unpublished density-one estimate from the authors' earlier preprint that, for almost all polynomials in the family, every rational point that is not twice another rational point has reduction height at least roughly $\log Ht(f)$; if that estimate fails, the canonical-height theorem collapses.
Editorial extensions
If this is right
- For the $c_1=0$ family, the naive height $h(P)$ is well-defined and satisfies $h(P)\ge(g-\epsilon)\log Ht(f)$ for every non-trivial rational point (Theorem 1.2).
- For every $f$ in the family and every $P\in J_f(\mathbb{Q})$, the canonical height satisfies $\widehat{h}_\Theta(P)\ge \tfrac12 h(P)-\tfrac{1}{12}g(7g+5)\log Ht(f)+c(g)$ (Theorem 1.3).
- As stated in the abstract, $100\%$ of all monic degree $2g+1$ polynomials would have $\widehat{h}_\Theta(P)\ge(\tfrac{3g-1}{4g(2g+1)}-\epsilon)\log|\Delta(f)|$ for every non-trivial $P$.
- The Kummer image is cut out scheme-theoretically by quadrics and quartics, with the ideal of quadrics independent of $f$, giving an explicit criterion for whether a point of projective space lies in $K_f(\mathbb{Q})$ and lifts to $J_f(\mathbb{Q})$.
- Duplication is computed by quartic polynomials, so the canonical height of a rational point can in principle be evaluated by repeatedly applying these polynomials to its Mumford triple.
Reading between the lines
- A reader should not count the abstract's all-monic statement as established: the body's Theorem 1.4 is stated only for the $c_1=0$ subfamily, and no argument transferring the density result to all monic polynomials under the $Ht$ ordering appears.
- If the imported reduction-height estimate of the earlier preprint is verified, the same method should apply to any height-ordered subfamily of monic polynomials that satisfies an analogous 'not too small, too often' estimate; the all-monic version would then follow.
- The Pfaffian coordinates and duplication polynomials should be directly implementable for genus at least $5$, extending the experimental range of explicit Kummer geometry beyond the currently worked cases $g=2,3$.
- The rank-at-most-one determinantal description of the Kummer image may be useful for sieve-style counting of rational points, because it replaces transcendental theta-function comparisons by algebraic inequalities in the Mumford coefficients.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper develops an explicit theory of the Kummer embedding for odd hyperelliptic Jacobians. For f(x)=x^{2g+1}+c_1x^{2g}+...+c_{2g+1} of nonzero discriminant, the authors construct a morphism Ψ:J→OGr(g,V) and show that composing with the spinor embedding of OGr(g,V) realizes the |2Θ|-linear system, giving a canonical basis for H^0(J,O_J(2Θ)) in terms of a Mumford representation. They further describe the theta group action via explicit matrices, prove the existence of quartic duplication polynomials, and show that the Kummer variety is cut out scheme-theoretically by quadrics and quartics. In the arithmetic part, they compare several height functions and prove a lower bound for the canonical height in terms of the naive height (Theorem 5.4), and state a density-one lower bound for canonical heights (Theorem 5.11) attributed to a combination of the present results with results from the authors' previous preprint [22].
Significance. If the height theorems were fully established, the paper would provide a density-one form of the Lang–Silverman conjecture for odd hyperelliptic Jacobians, a major advance. The explicit spinor/Clifford-algebra construction of the Kummer embedding and the duplication map is a substantial and original contribution: it gives, for all g, a canonical coordinate system on |2Θ|, explicit theta-group matrices, and a practical duplication algorithm, with a worked genus-4 example checked against Cantor's algorithm in Magma. These parts contain no fitted constants and are developed from scratch with careful sign conventions. The paper is therefore significant even aside from the height applications, and the explicit nature of the constructions is a definite strength.
major comments (3)
- [§5.3, proof of Theorem 5.11] The reduction to points outside 2J(Q) is invalid for torsion points. The proof says 'In view of the quadratic property of the height, it suffices to show that ... for all P ∈ J(Q) − 2J(Q)'; however, for a non-trivial point P of finite order, repeated halving never leaves 2J(Q), and the canonical height vanishes. Concretely, for g=1 and f(x)=x^3−432, the point P=(12,36) satisfies 2P=−P, so P∈2J(Q), and \widehat h_Θ(P)=0, while the asserted lower bound is (1−ϵ)\log Ht(f)>0 for small ϵ. Thus Theorem 5.11 as stated fails for any f with non-trivial rational torsion, and the proof provides no estimate showing that such f form a density-zero exceptional set. The theorem must either be restricted to non-torsion points or supplemented with a proof that 100% of f in F(X) have no non-trivial rational torsion.
- [§5.3, proof of Theorem 5.11] The proof imports two black-box statements from the authors' unpublished preprint [22]: [22, Corollary 3.11] and [22, Theorem 4.10], which together supply the density-one assertion that for almost all f, every P∈J(Q)−2J(Q) satisfies \widetilde h(P)>−\epsilon \log Ht(f). This external result is the only source of the '100%' conclusion for the points outside 2J(Q); no proof or independent verification is given in the present paper. If the reduction-height estimate in [22] fails, Theorem 5.11 collapses. The paper should either incorporate the necessary argument or state the theorem as conditional on [22].
- [Abstract and Theorem 1.4] The abstract claims the result for '100% of monic, degree 2g+1 polynomials f(x)∈Z[x]' with the bound in terms of \log|\Delta(f)|, but the body (Theorem 1.4 = Theorem 5.11) is proved only for the subfamily f(x)=x^{2g+1}+c_2x^{2g-1}+\cdots+c_{2g+1}, i.e., c_1=0, and with the bound in terms of \log Ht(f). Under the ordering Ht(f)=\max|c_i|^{1/i} used throughout, the c_1=0 subfamily has density zero among all monic degree 2g+1 polynomials, since c_1 ranges over O(X) values. Moreover, the sentence 'using the lower bound |\Delta(f)| \ll Ht(f)^{2g(2g+1)}' is backwards: this is an upper bound on |\Delta|, whereas passing from a lower bound in terms of \log Ht to one in terms of \log|\Delta| would require a lower bound of the form |\Delta(f)| \gg Ht(f)^{2g(2g+1)} on a density-one set, which is not proved. The abstract's headline claim is therefore unsupported by the arguments in the paper.
minor comments (3)
- [§4.3] The displayed Mumford triple for the example reads '(x4 + 4 + x3 + x2 + 2 + x + 3, ...)'; the ordering of terms is confusing and the constant appears to be misplaced. Please rewrite in standard polynomial notation.
- [§3.6] Proposition 3.18 is stated with 'We omit the proofs of these statements'; since this proposition is part of the paper's claimed results, it would be better to include at least a sketch or a precise reference for each assertion.
- [§5.3] The notation F_δ(X) is introduced after Theorem 5.11 but used in Proposition 5.12; consider moving the definition immediately before its first use to avoid confusion.
Circularity Check
The spinor/Kummer derivation is self-contained, but Theorem 5.11's 100% density conclusion imports its key reduction-height estimate from the authors' unpublished preprint [22]; separate non-circular gaps affect the abstract's all-monic claim and the torsion reduction.
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self citation load bearing
[Section 5.3, proof of Theorem 5.11 (also Introduction, Theorem 1.4)]
"In view of the quadratic property of the height, it suffices to show that a density 1 set of polynomials f (x) satisfy bhΘ(P ) ≥ ( 3g−1 2 − ϵ) Ht(f ) for all P ∈ J(Q) − 2J(Q). However, [22, Corollary 3.11] and [22, Theorem 4.10] together show that, for a density 1 set of polynomials f (x), all points P ∈ J(Q)−2J(Q) satisfy eh(P ) > −ϵ log Ht(f )."
The density-one part of the paper's main canonical-height theorem is not proved here; it is taken verbatim from [22], an unpublished preprint by the same two authors. The new work only supplies the comparison bh ≥ eh + (3g−1)/2 log X + ... in Lemma 5.13, and the '100%' premise itself is inherited from the cited [22, Cor. 3.11, Thm. 4.10]. If that reduction-height estimate fails, Theorem 5.11 collapses. This is load-bearing self-citation rather than an independent derivation, though it is not an equation-level equivalence by construction.
full rationale
Sections 2–4 develop the Kummer embedding, theta-group action, and duplication polynomials from first principles (Clifford algebras, pure spinors, Grothendieck–Riemann–Roch, generic spin bases), and these constructions do not reduce to the target height theorem. The circularity concern is concentrated in Section 5.3: the density-one statement for the canonical height is assembled from Lemma 5.13 plus the imported [22, Cor. 3.11, Thm. 4.10]. Because [22] is the authors' own unpublished preprint and no proof or independent verification is supplied, this is load-bearing self-citation; nevertheless the central new constructions are independent, so a score of 4 is appropriate. Two non-circular flags should be noted separately. First, the abstract claims 100% of all monic degree-(2g+1) polynomials, while Theorem 1.4 and Theorem 5.11 prove only the c1=0 subfamily; the sentence 'The statement in the abstract follows from this one, using the lower bound |Δ(f)| << Ht(f)^{2g(2g+1)}' only rescales the height and does not remove the c1=0 restriction. Second, the reduction 'it suffices' to P outside 2J(Q) fails for torsion points: a nontrivial torsion P has bhΘ(P)=0 and may be contained in 2J(Q) (all odd-order torsion is), so the quadratic-height descent never reaches the class covered by [22]. That is a correctness gap, not a circularity.
Assumptions & free parameters
assumptions (4)
- standard math Standard algebraic geometry: Riemann-Roch, Borel-Weil, Grothendieck-Riemann-Roch, Néron model theory, Mumford theta groups, and Riemann-Roch for singular curves.
- domain assumption The identification of J[2] with the centralizer of multiplication by x in SO(V), taken from [1, Proposition 11].
- domain assumption The density-one reduction-height lower bound from the authors' prior preprint [22, Corollary 3.11 and Theorem 4.10].
- domain assumption Density of the F_delta(X) family via the squarefree discriminant theorems [2, Theorem 4.4 and Theorem 5.4].
Cite this review
Pith. "Pith review of Kummers, spinors, and heights." pith.science (2026). https://pith.science/paper/IBEKKEQ2
@misc{pith2026250706865,
author = {Pith},
title = {Pith review of: Kummers, spinors, and heights},
year = {2026},
howpublished = {\url{https://pith.science/paper/IBEKKEQ2}},
note = {Machine review of arXiv:2507.06865}
}
abstract
Let $f(x) = x^{2g+1} + c_1 x^{2g} + \dots + c_{2g+1} \in k[x]$ be a polynomial of nonzero discriminant, and let $J$ denote the Jacobian of the odd hyperelliptic curve $C : y^2 = f(x)$. We show that the morphism $J \to \mathbb{P}^{2^g-1}$ associated to the linear system $|2 \Theta|$ may be described explicitly, for any $g \geq 1$, using the theory of pure spinors. We apply this theory to study the heights of rational points in $J(k)$, when $k$ is a number field. As a particular consequence, we show that $100\%$ of monic, degree $2g+1$ polynomials $f(x) \in \mathbb{Z}[x]$ of nonzero discriminant $\Delta(f)$ have the property that, for any non-trivial point $P \in J(\mathbb{Q})$, the canonical height of $P$ satisfies $ \widehat{h}_\Theta(P) \geq \left(\frac{3g-1}{4g(2g+1)} - \epsilon\right) \log | \Delta(f) |$. This is a `density 1' form of the Lang--Silverman conjecture.
Reference graph
Works this paper leans on
-
[22]
J. Laga and J. A. Thorne. 100% of odd hyperelliptic Jacobians have no rational points of small height. arXiv preprint, available athttps://arxiv.org/abs/2405.10224v1, 2025
arXiv 2025
-
[1]
Bhargava and B
M. Bhargava and B. H. Gross. The average size of the 2-Selmer group of Jacobians of hyperelliptic curves having a rational Weierstrass point. InAutomorphic representations andL-functions, volume 22 of Tata Inst. Fundam. Res. Stud. Math., pages 23–91. Tata Inst. Fund. Res., Mumbai, 2013
2013
-
[2]
Bhargava, A
M. Bhargava, A. Shankar, and X. Wang. Squarefree values of polynomial discriminants I.Invent. Math., 228(3):1037–1073, 2022
2022
-
[3]
C. Birkenhake and H. Lange.Complex abelian varieties, volume 302 ofGrundlehren der mathematischen Wissenschaften [Fundamental Principles of Mathematical Sciences]. Springer-Verlag, Berlin, second edition, 2004
work page 2004
- [4]
- [5]
-
[6]
E. Cartan. The theory of spinors. The M.I.T. Press, Cambridge, MA, 1967
work page 1967
-
[7]
J. W. S. Cassels and E. V. Flynn.Prolegomena to a middlebrow arithmetic of curves of genus2, volume 230 ofLondon Mathematical Society Lecture Note Series. Cambridge University Press, Cambridge, 1996
work page 1996
Show all 42 references
-
[8]
Chevalley
C. Chevalley. The algebraic theory of spinors and Clifford algebras. Springer-Verlag, Berlin, 1997. Collected works. Vol. 2, Edited and with a foreword by Pierre Cartier and Catherine Chevalley, With a postface by J.-P. Bourguignon
1997
-
[9]
B. Conrad. Reductive group schemes. InAutour des schémas en groupes. Vol. I, volume 42/43 ofPanor. Synthèses, pages 93–444. Soc. Math. France, Paris, 2014
2014
-
[10]
R. de Jong. On the Arakelov theory of elliptic curves.Enseign. Math. (2), 51(3-4):179–201, 2005
2005
-
[11]
U. V. Desale and S. Ramanan. Classification of vector bundles of rank2 on hyperelliptic curves.Invent. Math., 38(2):161–185, 1976/77
1976
-
[12]
R. Donagi. Group law on the intersection of two quadrics.Ann. Scuola Norm. Sup. Pisa Cl. Sci. (4), 7(2):217–239, 1980
1980
-
[13]
Duquesne
S. Duquesne. Calculs effectifs des points entiers et rationnels sur les courbes. Thèse de doctorat, Université Bordeaux, 2001
2001
-
[14]
T. A. Fisher and G. F. Sills. Local solubility and height bounds for coverings of elliptic curves.Math. Comp., 81(279):1635–1662, 2012
2012
-
[15]
Gruson, S
L. Gruson, S. V. Sam, and J. Weyman. Moduli of abelian varieties, Vinbergθ-groups, and free resolutions. In Commutative algebra, pages 419–469. Springer, New York, 2013
2013
-
[16]
Hartshorne
R. Hartshorne. Algebraic geometry. Graduate Texts in Mathematics, No. 52. Springer-Verlag, New York-Heidelberg, 1977
1977
-
[17]
D. Holmes. An Arakelov-theoretic approach to naïve heights on hyperelliptic Jacobians.New York J. Math., 20:927–957, 2014
2014
-
[18]
J.-i. Igusa. Theta functions. Die Grundlehren der mathematischen Wissenschaften, Band 194. Springer- Verlag, New York-Heidelberg, 1972. 57
1972
-
[19]
J. C. Jantzen.Representations of algebraic groups, volume 107 ofMathematical Surveys and Monographs. American Mathematical Society, Providence, RI, second edition, 2003
2003
-
[20]
G. R. Kempf. Multiplication over abelian varieties.Amer. J. Math., 110(4):765–773, 1988
1988
-
[21]
A. Khaled. Projective normality and equations of Kummer varieties.J. Reine Angew. Math., 465:197–217, 1995
1995
-
[23]
S. Lang. Fundamentals of Diophantine geometry. Springer-Verlag, New York, 1983
1983
-
[24]
Lockhart
P. Lockhart. On the discriminant of a hyperelliptic curve.Trans. Amer. Math. Soc., 342(2):729–752, 1994
1994
-
[25]
J. S. Müller. Explicit Kummer varieties of hyperelliptic Jacobian threefolds.LMS J. Comput. Math., 17(1):496–508, 2014
2014
-
[26]
D. Mumford. On the equations defining abelian varieties. I.Invent. Math., 1:287–354, 1966
1966
-
[27]
D. Mumford. Tata lectures on theta. I, volume 28 ofProgress in Mathematics. Birkhäuser Boston, Inc., Boston, MA, 1983. With the assistance of C. Musili, M. Nori, E. Previato and M. Stillman
1983
-
[28]
D. Mumford. Tata lectures on theta. II. Modern Birkhäuser Classics. Birkhäuser Boston, Inc., Boston, MA, 2007. Jacobian theta functions and differential equations, With the collaboration of C. Musili, M. Nori, E. Previato, M. Stillman and H. Umemura, Reprint of the 1984 original
2007
-
[29]
F. Pazuki. Theta height and Faltings height.Bull. Soc. Math. France, 140(1):19–49, 2012
2012
-
[30]
V. L. Popov. Picard groups of homogeneous spaces of linear algebraic groups and one-dimensional homogeneous vector fiberings.Izv. Akad. Nauk SSSR Ser. Mat., 38:294–322, 1974
1974
-
[31]
Ramanathan
A. Ramanathan. Equations defining Schubert varieties and Frobenius splitting of diagonals.Inst. Hautes Études Sci. Publ. Math., (65):61–90, 1987
1987
-
[32]
M. Reid. The complete intersection of two or more quadrics. PhD thesis, University of Cambridge, 1972
1972
-
[33]
Serre.Local fields, volume 67 ofGraduate Texts in Mathematics
J.-P. Serre.Local fields, volume 67 ofGraduate Texts in Mathematics. Springer-Verlag, New York-Berlin,
-
[34]
J. H. Silverman. Lower bounds for height functions.Duke Math. J., 51(2):395–403, 1984
1984
-
[35]
M. Stoll. On the height constant for curves of genus two.Acta Arith., 90(2):183–201, 1999
1999
-
[36]
M. Stoll. An explicit theory of heights for hyperelliptic Jacobians of genus three. InAlgorithmic and experimental methods in algebra, geometry, and number theory, pages 665–715. Springer, Cham, 2017
2017
-
[37]
A. Stubbs. Hyperelliptic curves. PhD thesis, University of Liverpool, 2000
2000
-
[38]
The Stacks project.https://stacks.math.columbia.edu, 2024
The Stacks project authors. The Stacks project.https://stacks.math.columbia.edu, 2024
2024
-
[39]
J. A. Thorne. A remark on the arithmetic invariant theory of hyperelliptic curves.Math. Res. Lett., 21(6):1451–1464, 2014
2014
-
[40]
X. Wang. Maximal linear spaces contained in the based loci of pencils of quadrics.Algebr. Geom., 5(3):359–397, 2018
2018
-
[41]
J. G. Zarhin and J. I. Manin. Height on families of abelian varieties.Mat. Sb. (N.S.), 89(131):171–181, 349, 1972. 58
1972
-
[1979]
Translated from the French by Marvin Jay Greenberg
Reviewed August 6, 2026 · model on record in the stance chip above.
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