Spans of Hecke points on modular curves
Spans of Hecke points on modular curves
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模曲线上 Hecke 点的跨度
DOI:
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发表时间:
2001
期刊:
影响因子:
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通讯作者:
B. Poonen
中科院分区:
文献类型:
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作者:
B. Poonen
We correct a theorem in the literature describing the rank of the span of the images of a point on a modular curve under Hecke correspondences. Let X be a modular curve over Q associated to one of the congruence subgroups Γ0(N), Γ1(N), or Γ(N). Assume that X has genus at least 2. Identify X with its image in the jacobian J under the map taking x to the class of x −∞, where ∞ ∈ X(Q) denotes the usual cusp. Let Jtors denote the torsion subgroup of J(Q). For any prime p not dividing N , the Hecke correspondence Tp on X induces an endomorphism τp of J . Finally, let ZTp(x) denote the Z-span in J(Q) of the p + 1 points of X(Q) obtained by applying Tp to x. The main result of this note is Theorem 2, which contradicts the following. Statement 1 (Theorem 0.4 in [Si2]). Let x ∈ X(Q) be a noncuspidal, non-CM point. Then for p sufficiently large, rank ZTp(x) = { p, if x ∈ Jtors. p + 1, otherwise. It is only the last sentence of the proof in [Si2] that is flawed: the “i(x) ∈ Jtors or τp = 0” on the left hand side of the last chain of equivalences should be replaced by “τp(i(x)) ∈ Jtors”. Therefore Statement 1 becomes true if “x ∈ Jtors” is replaced by “τpx ∈ Jtors”. Theorem 0.4 in [Si2] plays the role only of a remark: the main results of that paper, which are concerned with the heights of the images of a point under a Hecke correspondence, are unaffected by the correction. Silverman explained to me that he attributed Theorem 0.4 in [Si2] to “Mazur, unpublished” because Mazur sketched a statement and proof to him verbally; therefore he feels that Mazur should get credit for the idea, while he accepts responsibility for the minor error in its write-up. Theorem 2. Suppose that J is isogenous over Q to a product of elliptic curves E×F . Then there exist infinitely many nontorsion, noncuspidal, non-CM points x ∈ X(Q) such that there exist infinitely many primes p not dividing N for which rank ZTp(x) = p. Received October 23, 2001. 2000 Mathematics Subject Classification. Primary 14G35.