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2007.15180

ZARISKI DENSITY OF POINTS WITH MAXIMAL ARITHMETIC DEGREE

Kaoru Sano, Takahiro Shibata

wronghigh confidenceCounterexample detected
Category
math.DS
Journal tier
Strong Field
Processed
Sep 28, 2025, 12:55 AM

Audit review

The paper’s Question 1.5 asks whether (X,f) has densely many K-rational points with maximal arithmetic degree (disjoint orbits included), and Theorem 1.8 answers this affirmatively for every surjective self-morphism with δf>1 over a number field K. But this cannot hold in general: take an elliptic curve E/K with E(K) finite and f=[m] with m≥2; then δf=m^2>1 yet E(K) contains no Zariski-dense subset at all, contradicting Theorem 1.8. The proof of Section 3 in the paper appears to rely on constructing points of arbitrarily large extension degree (via a set T(D,A,B) defined in Lemma 3.3) and thus actually builds algebraic points over K̄, not K-rational points; Lemma 3.3 itself is stated with x∈X(K) but then uses [K(x):K]≫1, which is impossible for K-rational points and signals a notation/quantifier error in that section. Meanwhile, the paper’s other results (unirational: Theorem 1.11; abelian: Theorem 1.12; P1-bundles over elliptic curves: Theorem 6.1) align with the model’s weaker but correct statements about density after passing to a suitable finite extension. Thus the model’s counterexample and corrected scope are right, while the paper’s main Theorem 1.8 (as written) is false. Key loci: Definition 1.4 and Question 1.5 define the property and ask it over K; Theorem 1.8 claims a positive answer over K; Lemma 3.3 and the surrounding argument in Section 3 implicitly use algebraic points of large degree, not K-points. See the paper’s Definition 1.4, Question 1.5, and Theorem 1.8; and the density/proof devices in Lemma 3.1 and Lemma 3.3 (and Theorems 2.1–2.2 for canonical heights) for the mismatch between the statement and what is actually proved. The unirational/abelian cases (Theorems 1.11 and 1.12) and the P1-bundle case (Theorem 6.1) are consistent with the model’s summary. Citations: Definition 1.4 and Question 1.5, Theorem 1.8, Theorems 2.1–2.2, Lemmas 3.1 and 3.3, Theorems 1.11 and 1.12, Theorem 6.1, Abstract.

Referee report (LaTeX)

\textbf{Recommendation:} major revisions

\textbf{Journal Tier:} strong field

\textbf{Justification:}

The manuscript addresses the density of points with maximal arithmetic degree and develops robust tools (nef eigenclasses, canonical heights, selection lemmas) with meaningful applications to automorphisms, unirational varieties, and abelian varieties (with finite extensions). However, the headline theorem asserting K-rational density for all morphisms with δf>1 is false as stated and conflicts with basic counterexamples (e.g., elliptic curves with finite Mordell–Weil group). The Section 3 construction actually produces algebraic points over K̄ of large degree, not K-rational points, indicating a systematic notation/quantifier slip. If the general theorem is restated over K̄ (and K-rational claims restricted to the valid special settings), the paper would merit publication after careful revisions.