REVIEW 2 major objections 5 minor 36 references
Welschinger--Witt invariants
T0 review · 2 major / 5 minor · reviewed 2026-08-05 · deepseek-v4-flash
Pith's one-line read The paper proves that for k-rational del Pezzo surfaces of degree at least 6, quadratic Gromov–Witten invariants equal Welschinger–Witt invariants, and conjectures the equality for all rational surfaces.
desk verdict Welschinger–Witt invariants: a genuinely new bridge between real and quadratic Gromov–Witten counts, proved for degree ≥6 but conditional on three unpublished preprints. 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
Witt invariants of étale algebras in the sense of Serre: natural transformations Etn → W valued in Witt rings of quadratic forms. The paper uses the β-basis (βi) of the ring of such invariants; a Witt invariant is β-integral when its β-coefficients are integers. The Welschinger–Witt invariant V Wn,d is built from Welschinger invariants by the triangle recursion (a discrete version of Welschinger's formula), and the proof that quadratic Gromov–Witten invariants are also β-integral passes through essential marked floor diagrams whose quadratic multiplicities are expressed in the same β calculus.
What would settle it
Take k = F7, X = P^2_k, class d = 4 (so n0 = 11), and A = E_2 × E_3 × E_5 × E_7 × F7 in Et_11(F_7). Compute Q_{P^2,d,F7}(A) by enumerating the essential marked floor diagrams of Theorem 6.7 and sum their quadratic multiplicities over F7; compute V W_4(A) = 8β_1(A) + 2β_2(A) + β_3(A) with the β-basis of Section 2. The conjecture (and Theorem 6.1 for this case) holds exactly when the two Witt classes in W(F_7) agree.
Extended reading notes
Core claim
Central claim (Theorem 6.1): for blow-ups of P^2 in at most three points, the quadratic Gromov–Witten invariant Q_{n,d} — a partially defined Witt invariant — is the restriction of the Welschinger–Witt invariant V W_{n,d}. This is a case of Conjecture 5.14: Q_{X,D,k}(A0) = V W_{X,D}(A0) for every k-rational del Pezzo surface. The authors construct V W_{n,d} as a β-integral Witt invariant whose multireal values are Welschinger invariants, and show quadratic Gromov–Witten invariants are unramified Witt invariants away from 2 and 3. The proof reduces to toric surfaces via the quadratic Abramovich–Bertram formula and concludes β-integrality by floor diagram counts.
Load-bearing premise
The proof relies on Theorem 6.7: that quadratic Gromov–Witten invariants of toric del Pezzo surfaces are computed by summing the quadratic multiplicities of essential marked floor diagrams, with the large-characteristic assumption of the underlying floor-diagram computation removed.
Editorial extensions
If this is right
- If the conjecture is right, quadratic Gromov–Witten invariants of all k-rational del Pezzo surfaces are computed by the β-integral Welschinger–Witt invariants, whose inputs are only the real curve counts.
- The equality implies deformation invariance of quadratic Gromov–Witten invariants for rational del Pezzo surfaces, since V W depends only on the étale algebras of the points.
- Quadratic invariants in positive characteristic would be forced to agree with characteristic-zero values, a property the authors note is expected from construction.
- The floor-diagram formula provides an effective algorithm: essential marked floor diagrams with Witt-valued multiplicities compute both sides explicitly.
Reading between the lines
- If Conjecture 5.14 holds, every quadratic Gromov–Witten invariant of a k-rational surface is determined by signed counts of real curves, so computations over finite fields or p-adic fields can be replaced by real enumerative geometry.
- The β-integrality of Welschinger–Witt invariants imposes divisibility and congruence conditions on Welschinger invariants themselves—essentially a Witt-valued refinement of Welschinger's formula—that could be tested numerically on existing tables.
- The same triangle construction may apply to Welschinger invariants of P^3 and other Fano manifolds (as the paper sketches), predicting quadratic Gromov–Witten invariants of higher-dimensional varieties once the quadratic theory exists.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper proposes a conjectural relationship between Welschinger invariants, which are signed counts of real rational curves, and quadratic Gromov–Witten invariants, which are counts taking values in Witt–Grothendieck rings over general fields of characteristic not 2 or 3. The authors construct multivariable unramified Witt invariants from Welschinger invariants (Theorem 4.3), prove that quadratic Gromov–Witten invariants are Witt invariants and are unramified under appropriate hypotheses (Theorems 5.4 and 5.7), and formulate Conjecture 5.14 asserting equality of these two types of invariants for rational del Pezzo surfaces. The paper proves this conjecture for del Pezzo surfaces of degree at least 6 (Theorem 6.1), equivalent to blowing up at most three points, by reducing first to toric surfaces via a quadratic Abramovich–Bertram formula and then using a floor-diagram computation. The central theorem, Theorem 6.1, is thus built on the partially proven Theorem 6.7, which removes the large-characteristic assumption from the floor-diagram identity of [JPMPR25].
Significance. If the main theorem and conjecture hold, the paper provides a striking structural link: all quadratic Gromov–Witten invariants of k-rational surfaces would be determined by Welschinger invariants, packaged as β-integral Witt invariants. The construction of multivariable Witt invariants from Welschinger invariants, the multireal-triangle calculus, and the explicit tables of β- and λ-coefficients are valuable contributions in their own right. The paper is ambitious and introduces new tools that are likely to be influential. However, the central claim is conditional on the unproven details of Theorem 6.7 and on the availability and correctness of several unpublished preprints. The paper is not fully self-contained, and the proof of the key floor-diagram identity is only sketched.
major comments (2)
- [Section 6.1, Theorem 6.7] Theorem 6.7 is load-bearing: Corollary 6.8 and therefore Theorem 6.1 rest on the claim that the floor-diagram sum computes the quadratic Gromov–Witten invariant Q'^{(m-s)}_d. The proof given is a single paragraph asserting that both sides are unramified away from S={2,3} and then invoking the characteristic-0 result [JPMPR25, Theorem 10.13]. This is not sufficient as written. To make the spreading-out argument work, the authors must verify: (1) the left-hand side is unramified, which requires checking that the toric surface X_{k^3} has a smooth proper model over Z[1/6] and that Hypothesis 5.1 holds for the relevant divisor class; (2) the right-hand side is an S-integral Witt invariant on Sq_s — this is plausible since μ(D,φ) ∈ Z[t_1,…,t_s], but it is not demonstrated; and (3) the cited [JPMPR25, Theorem 10.13] indeed proves the identity as an equality of Witt invariants over Q, i.e., for
- [Section 6.2, Lemma 6.14] The positive-characteristic reduction in the proof of Lemma 6.14 is too compressed. The sentence 'Since the lemma holds in characteristic 0, it follows that the lemma holds for k perfect of positive characteristic as well' is only valid if both sides of the asserted equality are known to be unramified over the chosen DVR R, so that equality over the fraction field descends to the residue field. The proof should explicitly invoke Proposition 5.6, identify the model over R (the blow-up Bl_{E_{\tilde δ}×R} P^2_R), and check that the hypotheses of Proposition 5.6 are satisfied. As written, the descent step is asserted rather than demonstrated, which is a gap in a key reduction used in the proof of Theorem 6.1.
minor comments (5)
- [Throughout] There are several typos and inconsistencies: 'Weslchinger' for 'Welschinger' in Remark 4.12, 'Gomov' for 'Gromov' in Conjecture 5.14, and a garbled name in the acknowledgments ('BenoîtV WBertrand'). The notation Et_n(K) / Etn(K) is used inconsistently; please unify.
- [Section 2.3, Definition 2.15] The diagram in Definition 2.15 is hard to read: the placement of the isomorphism signs (∼=) is ambiguous. It should be clarified which arrows are isomorphisms and which are merely functoriality maps.
- [Section 6.2, proof of Theorem 6.1] After proving β-integrality of Q_{n,d,Q}, the proof states that the invariant 'must equal V W_{n,d}' by Theorem 4.3. This also uses Lemma 5.13 to identify the multireal values of Q_{n,d,Q} with those of V W_{n,d}; this step should be stated explicitly.
- [Section 6.1, proof of Corollary 6.8] The proof uses the identities t_j^2 = 2t_j and the identification of the basis {t_J} with the β-basis. These facts are used without reference; a pointer to Theorem 2.5 or Lemma 2.14 would help the reader.
- [General] The paper relies heavily on the unpublished preprints [KLSW23a], [BW25], and [JPMPR25]. While this is not a mathematical error, the authors should state in the introduction or in a remark exactly which results from these preprints are used and whether they are available in final form. This is particularly important for Theorem 6.7, which is a nontrivial generalization of [JPMPR25, Theorem 10.13].
Circularity Check
No circularity: the equality of quadratic Gromov–Witten and Welschinger–Witt invariants is proved via independent floor-diagram and Abramovich–Bertram inputs, not by construction or self-citation alone.
full rationale
The paper's central claim, Theorem 6.1, is that a partially defined quadratic Gromov–Witten invariant Q_{n,d} equals the Welschinger–Witt invariant V W_{n,d} for n1+...+nr ≤ 3. Neither side is defined in terms of the other: V W_{n,d} is built from Welschinger invariants via β-integral Witt invariants (Theorem 4.3), while Q_{X,D} is defined via the A1-degree of an oriented evaluation map (Section 5.1, following [KLSW23a]) and is shown independently to be a Witt invariant and unramified away from 2 and 3 (Theorems 5.4 and 5.7). The equality over R is an external theorem (Welschinger invariants as signatures of quadratic Gromov–Witten invariants, Lemma 5.13), and the hard part is β-integrality of Q, which is established by reducing to toric surfaces via the quadratic Abramovich–Bertram formula ([BW25], Lemma 6.14) and then applying the floor-diagram computation of [JPMPR25] (Theorem 6.7). The removal of the 'sufficiently large characteristic' assumption in Theorem 6.7 is a valid unramified specialization argument: both sides are unramified away from {2,3}, so equality in characteristic 0 implies equality in every residue characteristic not 2 or 3. This is not a fit or a renaming, nor does it assume the target equality. The self-citations to [KLSW23a], [KLSW23b], and [BW25] are used as external mathematical inputs; the cited statements do not include Conjecture 5.14 or Theorem 6.1, and the paper reproduces or sketches the relevant reductions rather than merely citing its own conclusion. Genuine limitations—such as the restriction to perfect fields, the lack of full deformation invariance, and the exclusion of characteristics 2 and 3—are explicitly acknowledged but are correctness or scope concerns, not circularity. No step was found in which the claimed prediction reduces by definition to the input data.
Assumptions & free parameters
assumptions (5)
- standard math Witt invariant structure theorem: Inv_k(n) is a free W(k)-module with beta-basis (Theorem 2.5, from [GMS03, Section 29]).
- domain assumption Existence and base-change properties of quadratic Gromov-Witten invariants, including the A1-degree of twisted evaluation maps over non-perfect fields (Definition 5.3, Lemma 5.2).
- domain assumption The quadratic Abramovich-Bertram formula of [BW25] applies to the blow-up families in Lemma 6.14.
- domain assumption The floor diagram computation of [JPMPR25, Theorem 10.13] computes Q'_{n,d}, with the large-characteristic assumption removed (Theorem 6.7).
- domain assumption Welschinger invariants satisfy the real Abramovich-Bertram formula (Theorem 4.1, from [Bru20, Proposition 2.3]).
Cite this review
Pith. "Pith review of Welschinger--Witt invariants." pith.science (2026). https://pith.science/paper/NAAZN7Q4
@misc{pith2026250904172,
author = {Pith},
title = {Pith review of: Welschinger--Witt invariants},
year = {2026},
howpublished = {\url{https://pith.science/paper/NAAZN7Q4}},
note = {Machine review of arXiv:2509.04172}
}
abstract
Welschinger invariants are signed counts of real rational curves satisfying contraints. Quadratic Gromov--Witten invariants give such counts over general fields of characteristic different from 2 and 3. For rational del Pezzo surfaces over a field, we propose a conjectural relationship between Welschinger and quadratic Gromov--Witten invariants. We construct multivariable unramified Witt invariants, in the sense of Serre, from Welschinger invariants and call them Welschinger--Witt invariants. We show that quadratic Gromov--Witten invariants are also Witt invariants and control their ramification. We then conjecture an equality between these Witt invariants, in particular giving a conjectural computation of all the quadratic Gromov--Witten invariants of $k$-rational surfaces. We prove this conjecture for $k$-rational del Pezzo surfaces of degree at least 6.
Figures
Reference graph
Works this paper leans on
-
[1]
Recursive formula for W elschinger invariants
Aubin Arroyo, Erwan Brugall\'e, and Luc\'ia L\'opez de Medrano. Recursive formula for W elschinger invariants. Int Math Res Notices , 5:1107--1134, 2011
work page 2011
-
[2]
Stable maps and H urwitz schemes in mixed characteristics
Dan Abramovich and Frans Oort. Stable maps and H urwitz schemes in mixed characteristics. In Advances in algebraic geometry motivated by physics ( L owell, MA , 2000) , volume 276 of Contemp. Math. , pages 89--100. Amer. Math. Soc., Providence, RI, 2001
work page 2000
-
[3]
Gromov-- W itten invariants in algebraic geometry
Kai Behrend. Gromov-- W itten invariants in algebraic geometry. Inventiones Mathematicae , 127(3):601--617, 1997
work page 1997
-
[4]
Pencils of quadrics and G romov- W itten- W elschinger invariants of C P ^3
Erwan Brugall \'e and Penka Georgieva. Pencils of quadrics and G romov- W itten- W elschinger invariants of C P ^3 . Math. Ann. , 365(1-2):363--380, 2016
work page 2016
-
[5]
Rational curves on del pezzo surfaces in positive characteristic
Roya Beheshti, Brian Lehmann, Eric Riedl, and Sho Tanimoto. Rational curves on del pezzo surfaces in positive characteristic. Trans. Amer. Math. Soc. Ser. B , 10(14):407--451, 2023
work page 2023
-
[6]
Stacks of stable maps and G romov-- W itten invariants
Kai Behrend and Yuri Manin. Stacks of stable maps and G romov-- W itten invariants. Duke Mathematical Journal , 85(1), 1996
work page 1996
-
[7]
okova geometry-topology conference, G\
Erwan Brugall \'e and Grigory Mikhalkin. Floor decompositions of tropical curves: the planar case. In Proceedings of the 15th G\"okova geometry-topology conference, G\"okova, Turkey, May 26--31, 2008 , pages 64--90. Cambridge, MA: International Press, 2009
work page 2008
-
[8]
Éléments de mathématique, 2,9: Algebre, Chapitre 9, Formes sesquilineares et formes quadratiques
Nicolas Bourbaki. Éléments de mathématique, 2,9: Algebre, Chapitre 9, Formes sesquilineares et formes quadratiques . Hermann, Paris, nouv. tirage edition, 1973
work page 1973
Show all 36 references
-
[9]
Surgery of real symplectic fourfolds and Welschinger invariants
Erwan Brugall \'e . Surgery of real symplectic fourfolds and Welschinger invariants. J. Singul. , 17:267--294, 2018
2018
-
[10]
On the invariance of W elschinger invariants
Erwan Brugall\'e. On the invariance of W elschinger invariants. Algebra i Analiz , 32(2):1--20, 2020
2020
-
[11]
A quadratic A bramovich-- B ertram formula
Erwan Brugallé and Kirsten Wickelgren. A quadratic A bramovich-- B ertram formula. 2025. Preprint , available at https://arxiv.org/abs/2506.17854
2025 arXiv
-
[12]
WDVV -type relations for Welschinger invariants: applications
Xujia Chen and Aleksey Zinger. WDVV -type relations for Welschinger invariants: applications. Kyoto J. Math. , 61(2):339--376, 2021
2021
-
[13]
Welschinger invariants of blow-ups of symplectic 4-manifolds
Yanqiao Ding and Jianxun Hu. Welschinger invariants of blow-ups of symplectic 4-manifolds. Rocky Mt. J. Math. , 48(4):1105--1144, 2018
2018
-
[14]
Cohomological invariants in G alois cohomology , volume 28 of University Lecture Series
Skip Garibaldi, Alexander Merkurjev, and Jean-Pierre Serre. Cohomological invariants in G alois cohomology , volume 28 of University Lecture Series . American Mathematical Society, Providence, RI, 2003
2003
-
[15]
Revêtements étales et groupe fondamental
Alexander Grothendieck and Michele Raynaud. Revêtements étales et groupe fondamental . Number 3 in Documents mathématiques. Soc. Mathématique de France, 2005. Éd. recomposée et annotée du vol. 224 des Lecture Notes in Mathematics publ. en 1971 par Springer-Verl
2005
-
[16]
Asaf Horev and Jake P. Solomon . The open G romov-- W itten-Welschinger theory of blow-ups of the projective plane . arXiv e-prints , October 2012
2012
-
[17]
Quadratically enriched plane curve counting via tropical geometry
Andrés Jaramillo Puentes, Hannah Markwig, Sabrina Pauli, and Felix Röhrle. Quadratically enriched plane curve counting via tropical geometry. February 2025
2025
-
[18]
Kiran S. Kedlaya. Swan conductors for p -adic differential modules. I . A local construction. Algebra Number Theory , 1(3):269--300, 2007
2007
-
[19]
Steven L. Kleiman. The P icard scheme. In Fundamental algebraic geometry , volume 123 of Math. Surveys Monogr. , pages 235--321. Amer. Math. Soc., Providence, RI, 2005
2005
-
[20]
Solomon, and Kirsten Wickelgren
Jesse Leo Kass, Marc Levine, Jake P. Solomon, and Kirsten Wickelgren. A quadratically enriched count of rational curves. Preprint ArXiv 2307.01936, 2023
2023
-
[21]
Solomon, and Kirsten Wickelgren
Jesse Leo Kass, Marc Levine, Jake P. Solomon, and Kirsten Wickelgren. A relative orientation for the moduli space of stable maps to a del pezzo surface. Preprint ArXiv 2307.01941, 2023
2023
-
[22]
Quadratic and H ermitian forms over rings , volume 294 of Grundlehren der Mathematischen Wissenschaften [Fundamental Principles of Mathematical Sciences]
Max-Albert Knus. Quadratic and H ermitian forms over rings , volume 294 of Grundlehren der Mathematischen Wissenschaften [Fundamental Principles of Mathematical Sciences] . Springer-Verlag, Berlin, 1991. With a foreword by I. Bertuccioni
1991
-
[23]
T. Y. Lam. Introduction to quadratic forms over fields , volume 67 of Graduate Studies in Mathematics . American Mathematical Society, Providence, RI, 2005
2005
-
[24]
Toward an algebraic theory of W elschinger invariants
Marc Levine. Toward an algebraic theory of W elschinger invariants. Preprint , available at https://arxiv.org/abs/1808.02238, 2018
2018 arXiv
-
[25]
Symmetric bilinear forms
John Milnor and Dale Husemoller. Symmetric bilinear forms . Springer-Verlag, New York-Heidelberg, 1973. Ergebnisse der Mathematik und ihrer Grenzgebiete, Band 73
1973
-
[26]
Gromov- W itten and Welschinger invariants of del Pezzo varieties
Thi-Ngoc-Anh Nguyen. Gromov- W itten and Welschinger invariants of del Pezzo varieties. Preprint, arXiv :2302.09412 [math. AG ] (2025), 2025
2025 arXiv
-
[27]
A purity theorem for the witt group
Manuel Ojanguren and Ivan Panin. A purity theorem for the witt group. Ann. Sci. \'Ecole Norm. Sup. , (4) 32(1):71--86, 1999
1999
-
[28]
Power structures on the grothendieck--witt ring and the motivic euler characteristic
Jesse Pajwani and Ambrus Pál. Power structures on the grothendieck--witt ring and the motivic euler characteristic. Ann. K-Th. 10 (2025) 123-152 , 10(2):123--152, March 2023
2025
-
[29]
Pandharipande, J
R. Pandharipande, J. Solomon, and J. Walcher. Disk enumeration on the quintic 3-fold. J. Am. Math. Soc. , 21(4):1169--1209, 2008
2008
-
[30]
Jake P. Solomon. Intersection theory on the moduli space of holomorphic curves with L agrangian boundary conditions. Thesis , available at https://arxiv.org/abs/math/0606429, 2006
2006 arXiv
-
[31]
Stacks project
The Stacks Project Authors . Stacks project. https://stacks.math.columbia.edu, 2025
2025
-
[32]
Enumerative invariants of stongly semipositive real symplectic six-manifolds
Jean-Yves Welschinger. Enumerative invariants of stongly semipositive real symplectic six-manifolds. Preprint, arXiv :math/0509121 [math. AG ] (2005), 2005
2005 arXiv
-
[33]
Invariants of real symplectic 4-manifolds and lower bounds in real enumerative geometry
Jean-Yves Welschinger. Invariants of real symplectic 4-manifolds and lower bounds in real enumerative geometry. Invent. Math. , 162(1):195--234, 2005
2005
-
[34]
Spinor states of real rational curves in real algebraic convex 3-manifolds and enumerative invariants
Jean-Yves Welschinger. Spinor states of real rational curves in real algebraic convex 3-manifolds and enumerative invariants. Duke Math. J. , 127(1):89--121, 2005
2005
-
[35]
Invariant count of holomorphic disks in the cotangent bundles of the two-sphere and real projective plane
Jean-Yves Welschinger. Invariant count of holomorphic disks in the cotangent bundles of the two-sphere and real projective plane. C. R. Math. Acad. Sci. Paris , 344(5):313--316, 2007
2007
-
[36]
Open Gromov - Witten invariants in dimension four
Jean-Yves Welschinger. Open Gromov - Witten invariants in dimension four. J. Symplectic Geom. , 13(4):1075--1100, 2015
2015
Reviewed August 5, 2026 · model on record in the stance chip above.
Discussion (0). Continue with ORCID to comment.