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Eta Products and Models for Modular Curves

Eta Products and Models for Modular Curves

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Cusps, as Families of Tate <strong>Curves</strong><br />

Definition: X 0 (N) is the projective curve whose points over C p<br />

correspond to pairs (E, C) where E is a generalized elliptic<br />

curve <strong>and</strong> C ⊆ E is a cyclic subgroup of order N which meets<br />

every component of E.<br />

Every cusp is surrounded by a family of Tate curves (with level<br />

structure) which degenerate into the corresponding Néron<br />

n-gon.<br />

Definition: For d|N, the canonical families of width d on X 0 (N)<br />

are given by (C ∗ p/q d , 〈ζq〉), where ζ is any primitive r th root of<br />

unity such that lcm(r, d) = N.

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