REVIEW 2 major objections 3 minor 28 references
Solubility of a family of conics with polynomial coefficients in many variables
T0 review · 2 major / 3 minor · reviewed 2026-08-03 · deepseek-v4-flash
Pith's one-line read For conic families with polynomial coefficients in many variables, the paper proves the count of parameters with a rational point is asymptotic to c B/(log B)^{3/2}, with c equal to the conjectured leading constant.
desk verdict The uniform count for diagonal conics in arithmetic progressions is a real contribution, but the final bridge that turns it into a family result is false, so the main theorem fails. 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 indicator ϑ_Q(t0,t1,t2), which is 1 exactly when the diagonal conic t0x0^2+t1x1^2=t2x2^2 has a nonzero rational point. The proof machinery is: a Birch system condition (enough variables relative to the degree so that a circle-method average is accurate), a recent circle-method theorem for averages of bounded arithmetic functions over polynomial values, an analytic averaging lemma that isolates the main coefficient in the average, and a product-over-primes computation of the local densities. An inclusion-exclusion step over common divisors converts sign-restricted coefficient counts into the full solubility count, yielding the final constant.
What would settle it
Compute, for a concrete homogeneous triple of polynomials and a point k where F0(k), F1(k), F2(k) are all positive and the conic F0(k)x0^2+F1(k)x1^2-F2(k)x2^2=0 has a rational point, the value of (1/2) Σ_ε 1_{min ε_jF_j(k)>0} ϑ_Q(ε0F0(k),ε1F1(k),ε2F2(k)). For example with F0=2X0, F1=X0, F2=3X0 and k=(1,0,...,0), the left side is 1/2 while the right side is 1; this would settle whether the proof's central identity holds.
Extended reading notes
Core claim
The central claim is Theorem 1.7: for homogeneous polynomials F0, F1, F2 of degree d that form a Birch system with smooth fibres and a complete-intersection common zero locus, the global solubility count N_glob(π_F,B) satisfies N_glob(π_F,B) ~ c(π_F) B/(log B)^{3/2}, with c(π_F) exactly the constant predicted by the fibration-families conjecture. Along the way, the paper proves a precise asymptotic for the proportion of diagonal ternary conics t0x0^2+t1x1^2+t2x2^2=0 with a rational point and with coefficients in arithmetic progressions, uniform in the modulus up to a power of log B. This arithmetic-progression theorem is the engine from which the main constant is assembled via local factors.
Load-bearing premise
The argument hinges on the identity that the count of rational points can be recovered by summing, over the three sign patterns that make the polynomial values all positive, the local solubility indicators and dividing by two; if that sign-bridge equality fails, the main theorem is not established.
Editorial extensions
If this is right
- If correct, the conjectured leading constant for fibrations is realized in this family: the power of log is 3/2 and the constant is a product of local densities.
- The uniform arithmetic-progression theorem for diagonal conics implies that the same constant governs counts for any modulus at most a small power of log B, allowing the circle-method averaging to be glued.
- The paper computes the relevant Galois cohomology invariant of the fibration (a Z/2 quotient generated by an explicit quaternion algebra), which fixes the Tamagawa-type factor in the constant.
- The result gives an additional example where the full constant, not just the logarithmic exponent, is verified for a family of conic bundles with polynomial coefficients in many variables.
- The method shows how to derive the constant from local factors c_8 and c_p defined by volumes of solubility regions, suggesting these local factors are the correct universal building blocks.
Reading between the lines
- The uniform arithmetic-progression theorem for diagonal conics could be imported to families of higher-dimensional quadrics or to fibrations over other bases, provided the circle-method averaging result is available.
- The computation of the constant as a product of local densities suggests that the same local factors appear in any proof of the fibration conjecture, so the shape of c(π_F) is robust even if the present proof is later modified.
- A direct numerical check of the sign-restricted identity for small-degree polynomial triples (e.g., triples of linear forms at a point with all values positive) would be a cheap way to validate the proof's central bridge before tackling the full theorem.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper studies the density of y ∈ P^n(Q) of bounded height for which the diagonal conic C_{F,y}: F_0(y)x_0^2 + F_1(y)x_1^2 = F_2(y)x_2^2 has a rational point. It claims an asymptotic N_glob(π_F,B) ~ c(π_F) B/(log B)^{3/2}, with the constant c(π_F) predicted by Loughran–Rome–Sofos. The proof combines a circle-method theorem of Destagnol–Lyczak–Sofos for averages over polynomial values with a new estimate (Theorem 4.2) for the number of soluble diagonal conics whose coefficients lie in arithmetic progressions, followed by a long computation of the resulting constant.
Significance. If the main theorem were correct, it would be a substantial confirmation of the Loughran–Rome–Sofos conjecture for a natural family of conic bundles, including the full leading constant. The paper contains a large amount of technical analytic number theory: a general Selberg–Delange lemma (Lemma 3.1), a careful application of the Destagnol–Lyczak–Sofos circle-method result, and an extensive computation of local constants. These components may be of independent interest. However, the central bridge connecting the sign-conditioned circle-method counts to the actual solubility count is invalid, so the claimed theorem is not established.
major comments (2)
- [Section 6, Eq. (6.5)] The displayed "Möbius inversion" identity is false. For a fixed primitive k, the condition min_j ε_j F_j(k)>0 is satisfied by the unique sign vector ε(k)=(sign F_0(k), sign F_1(k), sign F_2(k)). The summand is then (1/2)ϑ_Q(|F_0(k)|,|F_1(k)|,|F_2(k)|), not (1/2)ϑ_Q(F_0(k),F_1(k),F_2(k)). These differ on a set of positive density. Example within the theorem's hypotheses: n=3, F_0=X_0, F_1=X_1, F_2=X_0+X_1−X_2, k=(1,1,3,0). Then F(k)=(1,1,−1); the true conic x_0^2+x_1^2=−x_2^2 has no Q-point, while the selected ε=(+,+,−) gives x_0^2+x_1^2=x_2^2, which has (1,0,1). Hence the RHS of (6.5) receives a spurious contribution of 1/2. The failure is not a boundary effect; it occurs on the open region F_0>0,F_1>0,F_2<0. Moreover sign changes alter p-adic solubility (2x^2−y^2−3z^2=0 is anisotropic over Q_3, but 2x^2+y^2−3z^2=0 is soluble), so no local correction can be absorbed into the constant.
- [Section 6, final display] After substituting the asymptotic for N^1_ε into (6.5), the proof needs to sum over all eight ε. The displayed evaluation instead uses Σ_{ε≠±(1,1,−1)} vol(min_j ε_jF_j≥0)=c_8, i.e. it discards the two sign patterns ±(1,1,−1). These are exactly the patterns that made the bridge (6.5) false: on the positive-density region F_0>0,F_1>0,F_2<0 (and its negative), the selected ε is either (1,1,−1) or (−1,−1,1), and the corresponding N^1_ε count is nonzero because it counts positive-coefficient conics t_0x_0^2+t_1x_1^2=t_2x_2^2 with rational points. Dropping these terms silently changes the count from N_loc to a smaller set and is inconsistent with the preceding equality. The constant found is thus not the constant for the original family.
minor comments (3)
- [Section 4, Eq. (4.1)] The factor δ_p(n) for p∤q is introduced as 'the value of the factor corresponding to p in the Euler product in [16, th. 1.1]' before any computation. Since the subsequent Section 5 does derive this factor, the wording gives the impression that the conjectural constant is used as an input. Please rephrase or reorder so that the definition is presented as a summary of the calculation, not as an assumption.
- [Section 6, Lemma 6.8] The bound z ≤ sqrt((1/14) log_2 B) is stated without justification. It should be shown, or at least briefly explained, that this choice ensures W_z ≤ (log B)^{1/7} so that Theorem 4.2 applies.
- [Throughout] There are several typographical and language issues: leftover French phrases ('et', 'prouvée'), 'Belun' in Reference [26] should be 'Belin', and the notation c_8 vs c8 is used inconsistently. These are minor but should be corrected.
Circularity Check
No significant circularity: the final constant is computed from genuine local solubility densities; the one normalization imported from [16] is explicit and does not force the result. The serious problem at (6.5) is a correctness gap, not a circular reduction.
full rationale
The claimed derivation is not equivalent to its inputs. Theorem 4.2 is an auxiliary count for positive coefficient triples in arithmetic progressions; the local factor δ_p(n) for p∤q is explicitly chosen 'from the value of the factor corresponding to p in the Euler product in [16, th. 1.1]' (Remark after (4.1)). This is a transparent normalization, and it does not enter the final constant: in Lemma 6.8 the tail ∏_{p>z}(1-1/p)^{3/2}δ_p is 1+O(1/z), and Lemma 6.12 produces the genuine densities c_p=μ_p({t:ϑ_p(F(t))=1}). There is no self-citation: the author has no overlap with [5] or [16], and the external circle-method theorem [5, th. 2.4] is an independent input. The only load-bearing step that might look circular is (6.5), which claims N_loc equals a Möbius average of N1_ε defined via ϑ_Q(εF). For F0,F1>0>F2 the only contributing ε=(+,+,-) tests the indefinite conic F0x0^2+F1x1^2=(-F2)x2^2, whereas the original fibre is F0x0^2+F1x1^2=F2x2^2; these are not the same conic, so (6.5) is at best unproved and appears false. That invalidates the proof but is a correctness issue, not a reduction of the theorem to its own assumptions. Accordingly the circularity score is low.
Assumptions & free parameters
free parameters (3)
- m_p(z) = ⌊z⌋ + 2·1_{p=2} (Def. 6.1) =
m_2(z)=⌊z⌋+2, m_p(z)=⌊z⌋ for 3≤p≤z
- Exponent constraints q≤(log B)^{1/7} (Thm 4.2) and z≤(log_2 B)^{1/2}/√14 (Lemma 6.8) =
1/7, 1/14
- Truncation C=3 in Corollary 4.13 / Prop. 4.14 =
3
assumptions (6)
- standard math Multi-dimensional Selberg–Delange estimates (Tenenbaum [25, II.5])
- domain assumption Destagnol–Lyczak–Sofos circle-method theorem [5, th. 2.4] on averages of arithmetic functions over polynomial values (Birch system)
- standard math Hasse–Minkowski and Hilbert-symbol criteria for ternary quadratic forms ([22, ch. 3])
- domain assumption Large-sieve bounds of Friedlander–Iwaniec [6] and Wilson [28, lemma 5.1]
- standard math Geometric inputs: purity exact sequence [3, 3.7.2], [20, 2.6], exact sequence (2.1) from [14, (2.12)]
- ad hoc to paper Sign-splitting identity (1/2)Σ_ε 1_{min_j ε_jF_j>0}ϑ_Q(εF) = ϑ_Q(F) (eq. (6.5))
Cite this review
Pith. "Pith review of Solubility of a family of conics with polynomial coefficients in many variables." pith.science (2026). https://pith.science/paper/4SB3PXM7
@misc{pith2026251120282,
author = {Pith},
title = {Pith review of: Solubility of a family of conics with polynomial coefficients in many variables},
year = {2026},
howpublished = {\url{https://pith.science/paper/4SB3PXM7}},
note = {Machine review of arXiv:2511.20282}
}
abstract
We study the proportion of conics given by $(\mathcal{C}_{\mathbf{F}, \mathbf{y}}) : F_0(\mathbf{y})x_0^2 + F_1(\mathbf{y})x_1^2 = F_2( \mathbf{y})x_2^2 $ which have a rational point $\mathbf{x} = (x_0 :x_1:x_2) \in \mathbb{P}^2(\mathbb{Q})$, where $\mathbf{y} = (y_0 : \dots : y_n)\in \mathbb{P}^n(\mathbb{Q})$ and $F_0,F_1,F_2 \in \mathbb{Z}[X_0,\ldots, X_n]$ are homogeneous polynomials in many variables of the same degree $d$. We provide an asymptotic formula for the number of $\mathbf{y}$ of bounded height such that the corresponding conic $(\mathcal{C}_{\mathbf{F}, \mathbf{y}})$ has a rational point. In particular, our result agrees with the Loughran--Smeets and the Loughran--Rome--Sofos conjectures. Our strategy is based on a recent result of Destagnol--Lyczak--Sofos relying on the circle method to estimate the average of an arithmetic function over polynomials in many variables. To this end, we study the proportion of conics $t_0x_0^2 + t_1x_1^2 + t_2x_2^2 = 0$ having a rational point, and coefficients $t_0,t_1,t_2$ in arithmetic progressions.
Reference graph
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