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Heights of complete intersections in toric varieties

T0 review · 1 major / 4 minor · reviewed 2026-08-11 · deepseek-v4-flash

Pith's one-line read For two Laurent polynomials on a toric variety, the height of the intersection of their torsion-twisted hypersurfaces converges to an adelic sum of mixed integrals of roof functions and duals of Ronkin functions.

desk verdict The proof of Theorem B has a real gap at inequality (5.5), but the strategy and local results are solid; the paper needs revision before acceptance. read the letter →

arxiv 2412.16308 v2 pith:2UM3KQWS submitted 2024-12-20 math.AG math.NT

classification math.AGmath.NT MSC 14G4011G5014M2552A39
keywords toricvarietyheightofacompleteintersectionstrictsequencetorsionpointsRonkinfunctionmixedintegralArakelovgeometrylogarithmicequidistribution
verification ladder T0 review T1 audit T2 compute T3 formal

The pith

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The reading

The paper proves a limit formula for the height of the intersection of two hypersurfaces in a toric variety: twisting the defining Laurent polynomials by a quasi-strict sequence of torsion points, the height of the resulting 2-codimensional cycle converges to an adelic sum of mixed integrals of roof functions and convex duals of Ronkin functions. This is the k = 2 case of the authors' Conjecture A, which predicts that the typical arithmetic size of a complete intersection in a toric variety is determined entirely by convex-analytic data attached to the defining polynomials. The result matters because it extends the known height formulas for toric varieties and hypersurfaces to the first genuinely higher-codimensional situation, and it confirms a previously open conjecture for bivariate Fermat polynomials. The proof proceeds by decomposing the height into a well-understood hypersurface term plus local error terms, then showing each local error vanishes via logarithmic equidistribution of torsion points and a global adelic vanishing argument.

What carries the argument

The central object is the auxiliary function $$F_v(t) = \int_{$X_v^{{\mathrm{an}}$}} \log |t^*g|_v \, c_1(\overline{D}_{0,v}) \wedge \dots \wedge c_1(\overline{D}_{n-2,v}) \wedge \delta_{$Z_v^{{\mathrm{an}}$}},$$ where $Z$ is the hypersurface defined by $f$. Theorem 3.4 shows that $F_v$ extends to the whole analytic torus with at most logarithmic singularities along the closed subset where $t^*g$ is proportional to $f$: a function with at most logarithmic singularities is continuous outside that subset and bounded below near it by a constant times the logarithm of the maximum of the defining equations. At Archimedean places this extension uses a continuity theorem for fiber integrals, while at non-Archimedean places it uses a formal-model description of the Monge\,--Amp\`ere measure as a weighted sum over irreducible components of the special fiber. Combined with the Archimedean logarithmic equidistribution theorem for torsion points and the non-Archimedean theorem on linear forms in roots of unity, this makes each local error term tend to zero; a separate adelic argument using the Poisson formula for the sparse resultant bounds the sum over all but finitely many places.

What would settle it

For a fixed number field and a pair of Laurent polynomials $f,g$, compute the Galois-orbit average of the local function $I_v$ along a strict sequence of torsion points at a non-Archimedean place where the reduction of $f$ or $g$ is reducible; if that average does not tend to 0, or the explicit norm identity in Lemma 5.4 fails, then Theorem 4.4 and hence Theorem B would be false.

Watch

Extended reading notes

Core claim

The central claim (Theorem 6.2) is that for nonzero Laurent polynomials $f,g \in K[M]$ and any quasi-strict sequence of torsion points $(\omega_\ell)_\ell$ in $T(K)^2$, the height satisfies $$\lim_{\ell\to\infty} h_{D_0,\dots,D_{n-2}}\bigl(Z_T(\omega_{\ell,1}^* f,\omega_{\ell,2}^* g)\bigr) = \sum_{v\in M} n_v \, \mathrm{MI}_M\bigl(\vartheta_{D_0,v},\dots,\vartheta_{D_{n-2},v},\rho_{f,v}^\vee,\rho_{g,v}^\vee\bigr).$$ The left side is the height of the intersection cycle of two translated hypersurfaces inside a complete toric variety, and the right side is an adelic sum of mixed integrals of the $v$-adic roof functions of the metrized divisors and the convex duals of the $v$-adic Ronkin functions of $f$ and $g$. The theorem is proved by reducing to smooth projective toric data with very ample divisors and algebraic or smooth metrics, applying the arithmetic B\'ezout theorem to separate a hypersurface height, and then proving that the remaining local integrals vanish both at each place, by logarithmic equidistribution, and away from a finite set of bad places, by an adelic argument.

Load-bearing premise

The argument stands on the claim that, at every place, the local integral function $F_v$ extends from torsion points to the whole analytic torus with only logarithmic singularities; if that extension broke down at even one place, the local error terms would not vanish and the limit formula would collapse.

Editorial extensions

If this is right

  • For any two nonzero Laurent polynomials over a number field, the typical height of the intersection of their torsion-twisted hypersurfaces in a complete toric variety is explicitly computable from the Newton polytopes and the Ronkin data of $f$ and $g$.
  • The result settles the previously open case $k=2$ of Conjecture A and, for bivariate Fermat polynomials of arbitrary degrees, confirms the authors' earlier conjecture on limit heights.
  • Because the proof passes through reduction steps that allow arbitrary semipositive toric metrics to be approximated by smooth or algebraic ones, the formula holds for the full class of semipositive toric metrized divisors.
  • Averaging over strict sequences of finite sets of torsion points, the same limit describes the typical height and shows that almost all twists have height within any positive tolerance of the limit.

Reading between the lines

Editorial extensions of the paper, not claims the author makes directly.

  • The local extension theorem for the auxiliary function $F_v$ is the main technical bottleneck; the same strategy could in principle prove Conjecture A for $k>2$ once such an extension is available for $k$ polynomials.
  • Quantitative versions of the logarithmic equidistribution theorems used in the proof should yield explicit convergence rates for the height of twists of bounded torsion order, extending the special-case estimates the authors cite.
  • The limit formula suggests a convex-geometric picture of arithmetic complexity for complete intersections, analogous to the way sparse-resultant geometry computes typical degrees by mixed volumes; testing it on families with more than two polynomials or on non-split tori would be a natural next step.
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Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, and a circularity audit.

Referee Report

1 major / 4 minor

Summary. The paper proves Theorem B: for two nonzero Laurent polynomials f and g over a number field K, a complete toric variety X compactifying a split torus T, and a quasi-strict sequence of torsion points (ωℓ) in T(K)^2, the height of the intersection cycle ZT(ωℓ,1^* f, ωℓ,2^* g) converges to an adelic sum of mixed integrals of roof functions and Legendre–Fenchel duals of Ronkin functions. The proof combines toric intersection theory, arithmetic Bézout, an extension of an auxiliary function to the analytic torus with logarithmic singularities (Section 3), local logarithmic equidistribution theorems (Section 4), and an adelic vanishing statement (Section 5). The paper also contains a detailed reduction appendix and applications to average heights over torsion sets.

Significance. If the proof is completed, the result establishes a nontrivial two-codimensional case of the authors' conjecture and gives an arithmetic analogue of the Bernstein–Kushnirenko–Khovanskii theorem for typical intersections. The paper is well structured and makes use of deep external results (Stoll, Tate–Voloch, Dimitrov–Habegger) in a modular way, with most reduction steps moved to the appendix. The main technical concern is a specific false inequality in Section 5 that is used to prove the adelic vanishing; this gap appears fixable, but it is load-bearing for the proof of Theorem B.

major comments (1)
  1. [Section 5.B, Eq. (5.5)] The inequality (5.5) is false when the differences m−m' for m,m' in supp(f) generate a proper sublattice of M. For example, take K=Q, T=G_m^3, and f=g=1+x1+x2, which is absolutely irreducible and non-binomial. Let pℓ and qℓ be distinct primes with qℓ >> pℓ, and set ωℓ=(ζ_{pℓ}, ζ_{pℓ}^{ℓ}, ζ_{qℓ}). This sequence is strict: for every nonzero character (a,b,c), the value ζ_{pℓ}^{a+bℓ} ζ_{qℓ}^{c} is eventually different from 1, since for c≠0 the qℓ-component cannot cancel the pℓ-component once qℓ>|c|, while for c=0 the relation a+bℓ=0 holds for at most one ℓ. However dℓ=ord(ωℓ)=pℓ qℓ, whereas every character χ^{m−m'} with m,m'∈supp(f) involves only x1 and x2, so max_{m,m'} φ(ord(χ^{m−m'}(ωℓ))) = φ(pℓ) ≈ pℓ. This contradicts (5.5) for any c1≥1. Consequently the bound c2 log dℓ / dℓ^{c1} used to prove that the first summand in Theorem 5.2 tends to zero does not follow. The proof needs to replace dℓ by a quantity that measures the order of the projection of ωℓ to the subtorus generated by supp(f)−supp(f), or equivalently the lcm of the finitely many orders ord(χ^{m−m'}(ωℓ)), rather than the full order in T(K).
minor comments (4)
  1. [Introduction, p. 4] In the sentence 'we need to show prove that there exists a finite subset S ⊂ M', the word 'prove' appears to be a typographical error and should be deleted.
  2. [Section 4.A, proof of Theorem 4.1] In the phrase 'for all ℓ such that the strictness degree δ(ωℓ) si sufficiently large', 'si' should read 'is'.
  3. [Section 5.A, proof of Proposition 5.3] The final sentence 'the statement follows from Lemma 5.1' appears to cite the wrong lemma: Lemma 5.1 only establishes finiteness of S, whereas the displayed norm formula is proved in Lemma 5.4. The reference should be corrected.
  4. [Example 6.3] The notation 'MIZ2(0∆, ρ∨_{f,v}, ρ∨_{g,v})' is not defined in the paper; if it denotes the mixed integral for n=2 with the indicator of the standard simplex, this should be stated explicitly.

Circularity Check

0 steps flagged · score 0.0 of 10

No significant circularity: Theorem B is derived from prior k=0,1 height formulas plus new local and adelic vanishing arguments, and the target formula is never assumed.

full rationale

The paper's derivation chain is self-contained rather than circular. The proof of Theorem B (Theorem 6.2) follows the strategy in Section 2.B: the arithmetic B\'ezout formula gives the exact recursive identity in Proposition 2.5, separating the height into the hypersurface height h_{D0,...,D_{n-2},D_Ron_g}(Z_T(f)) plus a sum of local error terms. The first term is evaluated using Theorem 2.2 from [Gua18b], the previously established k=1 case whose hypotheses do not include the k=2 target. The remaining error terms are shown to vanish by two genuinely new inputs: Theorem 4.4, which combines the auxiliary-function regularity of Theorem 3.4 with the logarithmic equidistribution theorems of Dimitrov-Habegger and Tate-Voloch, and Theorem 5.2, the adelic vanishing argument. No equation defining the limit is inserted as an assumption, and no fitted quantity is renamed as a prediction. The self-citations to [BPS14] and [Gua18b] are legitimate prior published results used as base cases and technical tools; they do not presuppose Conjecture A or Theorem B. The challenged inequality (5.5) in Section 5.B is a potential correctness gap in the adelic vanishing proof, but a false estimate is not circularity: even if the bound fails, the target formula is not being used as its own input. Thus the score is 0.

Assumptions & free parameters 0 free parameters · 6 assumptions · 0 invented entities

No free parameters are fitted and no new entities are introduced. The proof combines prior results (arithmetic Bezout, equidistribution theorems, convex analysis of Ronkin functions) with new analytic estimates; the only novel objects (auxiliary function F_v, bad-place set S) are internal tools without independent physical or geometric meaning.

assumptions (6)
  • standard math Arithmetic Bezout formula for heights [BPS14, Chapter 1]
    Used in equation (2.3) to decompose the height of the intersection cycle into the height of the hypersurface plus local error terms.
  • standard math Stoll's theorem on the continuity of fiber integrals [Sto67]
    Used in Proposition 3.5 to prove archimedean continuity of the auxiliary function.
  • standard math Tate-Voloch theorem on linear forms in p-adic roots of unity [TV96]
    Used in Theorem 4.3 to establish non-archimedean logarithmic equidistribution of torsion points.
  • standard math Dimitrov-Habegger logarithmic equidistribution of torsion points [DH24]
    Used in Theorem 4.1 for the archimedean local vanishing of the error terms.
  • standard math Laurent's theorem (toric Manin-Mumford) [BG06, Theorem 7.4.7]
    Used in Corollary 1.9 to guarantee that quasi-strict sequences of torsion points eventually avoid the bad locus H.
  • standard math Poisson formula for the sparse resultant [DS15]
    Used in Proposition 3.8 to obtain the logarithmic lower bound for the auxiliary function.

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Pith. "Pith review of Heights of complete intersections in toric varieties." pith.science (2026). https://pith.science/paper/2UM3KQWS

@misc{pith2026241216308,
  author       = {Pith},
  title        = {Pith review of: Heights of complete intersections in toric varieties},
  year         = {2026},
  howpublished = {\url{https://pith.science/paper/2UM3KQWS}},
  note         = {Machine review of arXiv:2412.16308}
}
abstract

The height of a toric variety and that of its hypersurfaces can be expressed in convex-analytic terms as an adelic sum of mixed integrals of their roof functions and duals of their Ronkin functions. Here we extend these results to the $2$-codimensional situation by presenting a limit formula predicting the typical height of the intersection of two hypersurfaces on a toric variety. More precisely, we prove that the height of the intersection cycle of two effective divisors translated by a strict sequence of torsion points converges to an adelic sum of mixed integrals of roof and duals of Ronkin functions. This partially confirms a previous conjecture of the authors about the average height of families of complete intersections in toric varieties.

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