REVIEW 3 major objections 3 minor 1 cited by
Compactification Independence of the Irregular Hodge Filtration on Deligne-Mumford Stacks
T0 review · 3 major / 3 minor · reviewed 2026-08-07 · deepseek-v4-flash
Pith's one-line read The irregular Hodge filtration on a smooth Deligne–Mumford Landau–Ginzburg model is independent of the chosen compactification, making the orbifold irregular Hodge numbers invariants of the pair.
desk verdict The local root and blowup comparisons are solid and new; the global independence result is a well-argued reduction to an unverified Bergh–Rydh theorem, so referee it but make the dependency explicit. 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 carrying object is the Yu filtered complex $F^\lambda_{\mathrm{Yu}}K^a_{X,w} = \Omega^a_X(\log D)(\lfloor(a-\lambda)P\rfloor)$ for $a \geq \lceil\lambda\rceil$ and zero otherwise, whose hypercohomology image defines the filtration. To compare two compactifications the paper uses the Kontsevich lattices $\Omega^a_{X,w}(\alpha) = \ker(\nabla_w)$ inside the meromorphic de Rham complex; these lattices pull back functorially even when rounded Yu lattices do not, and the comparison is mediated by roofs through them. The geometric input is a filtered comparison for two elementary modifications — root constructions along boundary divisors and ordinary blowups of boundary-admissible centers — verified through an acyclic-defect criterion (vanishing of $R\pi_*$ of the cokernels). Global comparison then follows from two structural results: every rational compactification admits a good resolution by boundary-admissible blowups after toroidal strictification, and any two good compactifications are joined by a zigzag of such blowups and roots via relative stacky weak factorization.
What would settle it
Take a smooth proper Deligne–Mumford curve with two boundary components and a rational function $w$ with poles on both, form two compactifications by rooting different boundary components, and compute the level-$\lambda$ Yu images in $H^1(U,w)$; any discrepancy between the two subspaces, or any pair of good compactifications not joinable by boundary blowups and roots, would refute Theorem 5.6.
Extended reading notes
Core claim
The paper establishes compactification independence for the Yu irregular Hodge filtration in the setting of smooth separated Deligne–Mumford stacks of finite type over $\mathbb{C}$. Given a regular function $w$, twisted de Rham cohomology $H^k(U,w)$ carries, for each rational $\lambda$, a subspace $F^\lambda_{\mathrm{irr},X}H^k$ defined as the image of the hypercohomology of Yu's filtered complex $F^\lambda_{\mathrm{Yu}}K^\bullet_{X,w}$. Theorem 5.6(iv) asserts that for any two rational stack compactifications $X_1$ and $X_2$ these subspaces are literally equal inside $H^k(U,w)$, for all $k$ and $\lambda$; consequently the orbifold irregular Hodge numbers $f^{\lambda,\mu}_{\mathrm{orb}}(U,w)$ of Harder–Lee depend only on $(U,w)$ and not on any chosen compactification.
Load-bearing premise
The global comparison in Theorem 5.6 rests on the relative stacky weak factorization theorem of Bergh–Rydh, cited from an arXiv preprint and not proved or verified in the paper, together with Harper's strictification and Rydh's compactification results; if any of these unpublished results fail in the needed generality, the zigzag connecting two good compactifications may not exist and the theorem would not follow.
Editorial extensions
If this is right
- For every choice of compactifications of the inertia sectors, the age-shifted orbifold filtration $F^\lambda_{\mathrm{orb}}H^q_{\mathrm{dR,orb}}(U,w)$ is independent of the choice, so the Harder–Lee orbifold irregular Hodge numbers $f^{\lambda,\mu}_{\mathrm{orb}}(U,w)$ are invariants of the pair $(U,w)$ alone.
- The stacky Clarke mirror formula of Harder–Lee becomes a statement about invariants rather than about chosen compactifications, since both sides are now well-defined without auxiliary data.
- Any two compactifications produce filtered spectral sequences that agree from the $E_1$ page onward; in particular, degeneration at $E_1$ is a property of the Landau–Ginzburg model, not of the compactification.
- Good stack compactifications exist for every smooth separated Deligne–Mumford Landau–Ginzburg model, and projective good compactifications exist whenever the coarse moduli space is quasi-projective, so the invariants are computable in practice.
Reading between the lines
- A natural testable extension, not pursued in the paper, is whether compactification independence persists in smooth families of Landau–Ginzburg models; if it does, the orbifold irregular Hodge numbers would vary flatly and could be computed at any special fibre.
- The acyclic-defect criterion isolates the exact vanishing that makes each elementary modification invisible to the filtration; the same criterion could be reused to test other modifications, such as weighted or non-smooth toroidal blowups, whenever the corresponding defect vanishing can be verified.
- Because the theorem works with rational extensions of $w$ and permits zero–pole intersections satisfying the Chen–Yu normal form, computational recipes for irregular Hodge numbers can now be run on any convenient normal-crossing compactification, including ones where the potential is not a morphism.
- The sectorwise application suggests that orbifold irregular Hodge numbers could be studied one inertia component at a time, keeping only the age shift and the restricted potential; the paper does not explore whether such sectorwise invariants satisfy further structural identities such as symmetries under crepant resolutions.
Signed reviews
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper studies the irregular Hodge filtration on the twisted de Rham cohomology of a smooth separated Deligne-Mumford Landau-Ginzburg model (U,w). It introduces NC rational stack compactifications, in which the potential w extends only rationally and is required to satisfy a local nondegeneracy condition near its polar divisor. It defines the Yu-type filtered complex and the Kontsevich lattices on such compactifications, and the main theorem (Theorem 5.6) asserts that the resulting filtration on H^k(U,w) is independent of the compactification. The proof reduces the comparison to an acyclic-defect criterion (Proposition 3.13), establishes filtered comparison for boundary roots (Theorem 4.4) and for boundary-admissible blowups (Theorem 4.11), resolves every NC rational compactification to a good stack compactification (Theorem 5.3), and finally invokes a relative stacky weak factorization (Theorem 5.5) to connect any two good compactifications. Corollary 5.7 transfers this independence to the orbifold irregular Hodge numbers of Harder and Lee via inertia sectors and age shifts.
Significance. If the main theorem is valid, it extends Yu's and Chen-Yu's compactification independence from smooth varieties to Deligne-Mumford stacks and makes the Harder-Lee orbifold irregular Hodge numbers invariants of the Landau-Ginzburg model, which is a meaningful step for stacky mirror symmetry. The paper's own local contributions are substantial: the roof construction via Kontsevich lattices cleanly handles zero-pole cancellation, the acyclic-defect criterion is a useful organizing principle, and the root and blowup comparisons are carried out with explicit defect filtrations and appear internally coherent. There is no circularity in the argument: independence is obtained from explicit quasi-isomorphisms, with external results used as tools. However, the global conclusion currently rests on substantial unpublished external inputs, most importantly the Bergh-Rydh weak factorization theorem, whose hypotheses are not verified in the manuscript.
major comments (3)
- [§5.4, Theorem 5.5] The global zigzag connecting two arbitrary good stack compactifications is asserted by direct citation to the unpublished arXiv preprint [BR19, Theorem D], with the paper's own proof consisting of a short paragraph that does not state the hypotheses of that theorem. This is load-bearing: Theorem 5.5 is the only bridge between two arbitrary good models, and Theorem 5.6(iv) inherits all of its risk. In particular, Definition 2.3 only requires properness, and the paper explicitly notes that the coarse moduli space need not be projective, while many available weak factorization statements are formulated under projectivity or global-quotient hypotheses. The published global-quotient case [Ber18] does not cover the stated generality. The authors should quote [BR19, Theorem D] with its full hypotheses and verify them for good stack compactifications, provide a proof of Theorem 5.5, or restrict the main theorem to a class for which the factorization is established.
- [§5.2–§5.3, Theorems 5.3 and 5.4] The reduction to good compactifications depends on Harper's unpublished strictification [Har17, Lemmas A.2.4 and A.2.6] and, for the existence statement, on Rydh's unpublished draft [Ryd11, Theorem F]. These are not bibliographic details: Proposition 5.2 and Theorem 5.3 need the specific centers produced by Harper's cone-complex construction to be boundary strata preserving the polar normal form, and Proposition 5.4 needs the full force of Rydh's compactification theorem. The manuscript gives no independent verification of these inputs. If these results are not available in a stable, verifiable form, the resolution theorem and the sectorwise existence used in Corollary 5.7 are not self-contained. The authors should make the precise statements of the cited results available in an appendix or replace them with proofs.
- [§3.5, Theorem 3.17] The advertised application to Harder-Lee orbifold irregular Hodge numbers depends on the identification of their sector complexes with the Yu complexes. The proof of Theorem 3.17 asserts that Harder-Lee's explicit Yu-complex formula is 'termwise the complex of Definition 3.2' and appeals to Lemma 3.16(ii), but the passage from Harder-Lee's nondegeneracy conditions, which include a global irreducibility requirement on the zero divisor, to the paper's weaker NC rational condition is only explained in an informal paragraph before Definition 3.15. Since the restriction of the zero divisor to an inertia sector can split or become empty, this is a real convention rather than an immediate consequence. The identification in Theorem 3.17 should be proved in detail, or explicitly stated as an additional assumption on the Harder-Lee compactifications.
minor comments (3)
- [Throughout] The text contains many encoding artifacts and typos (for example 'èsimultaneous', 'ètale', 'trange') that should be cleaned before publication.
- [§2.2, Definition 2.3] The terminology 'NC rational', 'strict', 'morphic', and 'good' is introduced in quick succession; a short glossary or summary table of the four levels would improve readability, especially since several theorems mix these adjectives.
- [References] The references [BR19], [Har17], and [Ryd11] are listed as unpublished preprints or preliminary drafts; please update to published versions if they exist, otherwise state their status and provide stable identifiers.
Circularity Check
No circularity found: the compactification independence theorem is proved by explicit filtered quasi-isomorphisms for elementary modifications, and the global zigzag is imported as an external geometric factorization result, not assumed from the target conclusion.
full rationale
The paper's derivation chain is: define the Yu filtration on any NC rational stack compactification; prove filtered comparison under the two elementary modifications (boundary roots and boundary-admissible blowups) via explicit Kontsevich-lattice defect computations (Theorems 4.4 and 4.11); resolve an arbitrary NC rational compactification to a good one by strictification and zero–pole blowups (Theorem 5.3); join any two good compactifications by a zigzag supplied by Bergh–Rydh relative stacky weak factorization (Theorem 5.5); and compose the comparisons to obtain equality of image subspaces (Theorem 5.6). No step defines the desired independence into the filtration or into a fitted parameter. In particular, Theorem 5.5 is presented as an external geometric input: the paper explicitly cites [BR19, Theorem D] and notes the published global-quotient case [Ber18]. Even if this external theorem is heavy or its hypotheses are not fully checked, relying on an independent geometric statement is dependency, not circularity. The local comparisons are also not assumed: the acyclic-defect criterion (Proposition 3.13) is verified by computing and killing exceptional cokernels, and Corollary 3.11 converts the resulting quasi-isomorphisms into equality of cohomological images. There is no fitted input later relabeled as a prediction, no self-citation load-bearing for the central claim, and no renaming of a known empirical pattern as an organizing principle. The paper is not fully self-contained because it leans on unpublished or preprint results, but that is a correctness-risk issue, not circularity.
Assumptions & free parameters
assumptions (9)
- standard math Deligne's logarithmic comparison theorem for NC boundaries and connections with zero residues.
- domain assumption Chen-Yu local Kontsevich-Yu comparison ([CY18, Proposition 1(ii)]).
- standard math Cadman's root stack description (quotient chart, properness, complement behavior).
- standard math AOV tame pushforward exactness for finite linearly reductive stabilizers.
- domain assumption Harper's toroidal boundary strictification ([Har17, Lemmas A.2.4 and A.2.6]).
- domain assumption Bergh-Rydh relative stacky weak factorization ([BR19, Theorem D]).
- domain assumption Rydh's compactification theorem for tame Deligne-Mumford stacks ([Ryd11, Theorem F]).
- domain assumption Temkin's functorial desingularization with boundary for algebraic stacks ([Tem18, Theorems 1.1.11 and 1.1.13(i)]).
- domain assumption Kresch's quotient and projective compactification results for Deligne-Mumford stacks ([Kre09, Theorems 4.4 and 5.3]).
Cite this review
Pith. "Pith review of Compactification Independence of the Irregular Hodge Filtration on Deligne-Mumford Stacks." pith.science (2026). https://pith.science/paper/AOOOUTUV
@misc{pith2026260806234,
author = {Pith},
title = {Pith review of: Compactification Independence of the Irregular Hodge Filtration on Deligne-Mumford Stacks},
year = {2026},
howpublished = {\url{https://pith.science/paper/AOOOUTUV}},
note = {Machine review of arXiv:2608.06234}
}
abstract
Let $(\mathscr U,w)$ be a smooth separated Deligne--Mumford stack of finite type over $\mathbb C$, with a regular function $w$. Following Yu, one can use a compactification to define a filtration on its twisted de Rham cohomology. The same compactification gives Kontsevich lattices that compute this filtration. The extension of $w$ on the compactification may be only rational. Only a local nondegeneracy condition near the polar divisor is imposed. We prove that the resulting filtration does not depend on the compactification. The proof uses good resolutions and stacky weak factorization. This reduces the comparison to blowups and roots along boundary divisors. Filtered comparison theorems for the Yu and Kontsevich complexes are established for both operations. Harder and Lee use orbifold irregular Hodge numbers in their study of stacky Clarke mirror pairs. Compactification independence applies sector by sector to their setting. Thus the resulting orbifold filtration and irregular Hodge numbers depend only on the stack Landau--Ginzburg model.
Forward citations
Cited by 1 Pith paper
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$E_1$-Degeneration for Irregular Hodge Filtrations on Deligne--Mumford Stacks
For every smooth separated Deligne-Mumford stack with quasi-projective coarse space, the irregular Hodge filtration degenerates at E1 on every good stack compactification.
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