Recognition: unknown
Birational boundedness of stable families
Pith reviewed 2026-05-08 02:10 UTC · model grok-4.3
The pith
Algebraically integrable foliations of fixed dimension and bounded adjoint volume are log birationally bounded.
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
Core claim
We prove that algebraically integrable foliations of fixed dimension and bounded adjoint volume are log birationally bounded. This stronger statement implies that normal projective stable families of maximal variation, of fixed dimension, and with bounded adjoint volume are birationally bounded. In this way, the birational geometry of foliations provides a systematic framework for approaching classical boundedness problems for fibrations. A key input is our proof of McKernan's ACC conjecture for interpolated log canonical thresholds of algebraically integrable foliations.
What carries the argument
Log birational boundedness for algebraically integrable foliations of fixed dimension and bounded adjoint volume, which reduces boundedness questions for fibrations to the birational geometry of foliations.
If this is right
- Stable families of maximal variation with bounded adjoint volume are birationally bounded in fixed dimension.
- Birkar's and Jiang's boundedness criteria hold for Fano algebraically integrable adjoint foliated structures.
- Adjoint volumes admit lower bounds, automorphism groups are bounded, and ACC theorems hold for pseudo-effective thresholds, R-complementary thresholds, and the Fano spectrum.
Where Pith is reading between the lines
- The foliation framework may supply a route to boundedness statements for families that are not stable or do not have maximal variation.
- Explicit examples of foliations satisfying the ACC could be used to test whether the volume bound is sharp.
Load-bearing premise
The ascending chain condition holds for interpolated log canonical thresholds of algebraically integrable foliations.
What would settle it
An infinite sequence of pairwise non-birational algebraically integrable foliations of fixed dimension, all with bounded adjoint volume, would falsify the central claim.
Figures
read the original abstract
We prove that normal projective stable families of maximal variation, of fixed dimension, and with bounded adjoint volume are birationally bounded. This is a consequence of a substantially stronger statement, formulated a priori independently of stable families: algebraically integrable foliations of fixed dimension and bounded adjoint volume are log birationally bounded. In this way, the birational geometry of foliations provides a systematic framework for approaching classical boundedness problems for fibrations. A key input is our proof of M\textsuperscript{c}Kernan's ACC conjecture for interpolated log canonical thresholds of algebraically integrable foliations. This may be viewed as the foliated analogue of Shokurov's ACC conjecture for log canonical thresholds, proved in the classical setting by Hacon--M\textsuperscript{c}Kernan--Xu. As applications, we establish two boundedness criteria for Fano algebraically integrable adjoint foliated structures: Birkar's criterion for exceptional Fanos, and Jiang's criterion for Fanos for which both Tian's $\alpha$-invariant and the anti-canonical volume are bounded away from zero. We also obtain several results on the birational geometry of algebraically integrable adjoint foliated structures, including lower bounds for adjoint volumes, boundedness of automorphism groups, and ACC theorems for pseudo-effective thresholds, $\mathbb{R}$-complementary thresholds, and the Fano spectrum.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper proves that normal projective stable families of maximal variation, fixed dimension, and bounded adjoint volume are birationally bounded. This follows from the stronger claim that algebraically integrable foliations of fixed dimension and bounded adjoint volume are log birationally bounded. The key technical step is a proof of McKernan's ACC conjecture for interpolated log canonical thresholds on algebraically integrable foliations (the foliated analogue of the Hacon-McKernan-Xu theorem). Applications include Birkar's and Jiang's criteria for Fano algebraically integrable adjoint foliated structures, lower bounds on adjoint volumes, boundedness of automorphism groups, and ACC results for pseudo-effective thresholds, R-complementary thresholds, and the Fano spectrum.
Significance. If the central claims hold, the work supplies a new systematic framework that reduces classical boundedness questions for stable families and fibrations to questions about algebraically integrable foliations. It extends the classical ACC theorem to the foliated setting and derives several new boundedness and ACC statements for adjoint foliated structures. The approach is a priori independent of the stable-family statement and may influence future work on moduli spaces of varieties and foliations.
major comments (2)
- [§3, Theorem 3.1] §3, Theorem 3.1 (the foliated ACC statement): the reduction from the interpolated log canonical threshold to the classical lc threshold via the algebraically integrable foliation structure appears to rely on a specific choice of resolution; the manuscript should explicitly verify that the ACC holds independently of the choice of log resolution used to define the interpolated threshold.
- [§5.2] §5.2, the proof of log birational boundedness for foliations: the argument invokes a uniform lower bound on the adjoint volume to obtain a uniform bound on the number of components of the discriminant; it is not immediately clear whether this bound remains effective when the foliation is only assumed to be algebraically integrable rather than coming from a fibration with maximal variation.
minor comments (2)
- [§2] The notation for the interpolated log canonical threshold (e.g., the symbol lct_α) is introduced without a dedicated definition paragraph; a short subsection collecting all threshold notations would improve readability.
- [Figure 1] Figure 1 (the diagram illustrating the reduction from stable families to foliations) uses arrows whose labels are not explained in the caption; adding a sentence clarifying the meaning of each arrow would help readers unfamiliar with the foliation dictionary.
Simulated Author's Rebuttal
We thank the referee for the careful reading of the manuscript and the constructive comments. We address each major comment below and will incorporate clarifications in the revised version.
read point-by-point responses
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Referee: [§3, Theorem 3.1] §3, Theorem 3.1 (the foliated ACC statement): the reduction from the interpolated log canonical threshold to the classical lc threshold via the algebraically integrable foliation structure appears to rely on a specific choice of resolution; the manuscript should explicitly verify that the ACC holds independently of the choice of log resolution used to define the interpolated threshold.
Authors: We thank the referee for this observation. The interpolated log canonical threshold for an algebraically integrable foliation is in fact independent of the choice of log resolution: if two resolutions are given, they admit a common refinement on which the discrepancies with respect to the foliated pair coincide by the definition of algebraic integrability and the pull-back formula for the canonical class of the foliation. Consequently the ACC statement in Theorem 3.1 holds uniformly. To make this explicit we will insert a short paragraph immediately after the definition of the interpolated threshold in §3. revision: yes
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Referee: [§5.2] §5.2, the proof of log birational boundedness for foliations: the argument invokes a uniform lower bound on the adjoint volume to obtain a uniform bound on the number of components of the discriminant; it is not immediately clear whether this bound remains effective when the foliation is only assumed to be algebraically integrable rather than coming from a fibration with maximal variation.
Authors: The argument in §5.2 relies solely on algebraic integrability together with the uniform lower bound on adjoint volume furnished by the ACC for interpolated thresholds (Theorem 3.1). No use is made of the maximal-variation hypothesis that appears only in the application to stable families. The bound on the number of discriminant components is obtained by the same volume comparison that works for any algebraically integrable foliation; the maximal-variation case is merely a special instance. We will add one clarifying sentence at the beginning of the proof in §5.2 to emphasize this generality. revision: yes
Circularity Check
No significant circularity detected
full rationale
The derivation proceeds by first proving McKernan's ACC conjecture for interpolated log canonical thresholds on algebraically integrable foliations as an independent result (modeled on the classical Hacon-McKernan-Xu theorem), then using this to establish the stronger log birational boundedness for such foliations of fixed dimension and bounded adjoint volume, from which the birational boundedness of stable families follows formally. No load-bearing step reduces by construction to a fitted parameter, self-definition, or self-citation chain; the foliated ACC and boundedness statements are presented as a priori independent of the target family result, with all cited prior work (e.g., classical ACC) external and non-overlapping in a way that would force the conclusion.
Axiom & Free-Parameter Ledger
Reference graph
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discussion (0)
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