## On elliptic curves with complex multiplication as factors of the Jacobians of modular function fields.(English)Zbl 0225.14015

As Hecke showed, every $$L$$-function of an imaginary quadratic field $$K$$ with a Größencharacter $$\lambda$$ is the Mellin transform of a cusp form $$f(z)$$ belonging to a certain congruence subgroup $$\Gamma$$ of $$\mathrm{SL}_2(\mathbb Z)$$. After a suitable normalization of $$\lambda$$, $$\Gamma$$ is given by
$\Gamma = \left\{ \begin{pmatrix}{a &b\\ c &d}\end{pmatrix} \in \mathrm{SL}_2(\mathbb Z)\mid a\equiv d\equiv 1,\;c\equiv 0\pmod{D\cdotN(c)}\right\},$
where $$-D$$ is the discriminant of $$K$$ and $$c$$ is the conductor of $$\lambda$$. If the weight of $$f(z)$$ is $$2$$, $$f(z)\,dz$$ is a differential form of the first kind on the compactification $$(H/\Gamma)^*$$ of the quotient $$H/\Gamma$$, where $$H$$ denotes the upper half complex plane. Denote by $$\mathrm{Jac}(H/\Gamma)$$ the Jacobian variety of $$(H/\Gamma)^*$$, and identify the tangent space of $$\mathrm{Jac}(H/\Gamma)$$ at the origin with the space of all differential forms of the first kind on $$(H/\Gamma)^*$$. Let $$A$$ be the smallest abelian subvariety of $$\mathrm{Jac}(H/\Gamma)$$ that has $$f(z)\,dz$$ as a tangent at the origin. The author proves the following result:
The abelian variety $$A$$ is a product of copies of an elliptic curve whose endomorphism algebra is isomorphic to $$K$$.
Let $$E$$ be an elliptic curve defined over $$\mathbb Q$$ such that $$\mathrm{End}_{\mathbb Q}(E)$$ is isomorphic to $$K$$. As Deuring showed, the zeta-function of $$E$$ over $$\mathbb Q$$ is exactly the $$L$$-function of a certain Größencharacter $$\lambda$$ of $$K$$. The author obtains an abelian variety $$A$$ by a procedure described by the following scheme:
elliptic curve $$E\mapsto$$ zeta-function with a Größencharacter $$\lambda\mapsto$$ cusp form $$f(z)\mapsto$$ abelian subvariety $$A$$ of $$\mathrm{Jac}(H/\Gamma')$$,
where the group $$\Gamma'$$ is of the form:
$\Gamma' = \left\{ \begin{pmatrix}{a &b\\ c &d}\end{pmatrix} \in \mathrm{SL}_2(\mathbb Z)\mid c\equiv 0\pmod{D\cdotN(c)}\right\},$
and proves the following result:
$$A$$ is an elliptic curve isogenous to $$E$$ over $$\mathbb Q$$.

### MSC:

 11F03 Modular and automorphic functions 14H05 Algebraic functions and function fields in algebraic geometry 14H52 Elliptic curves 11G05 Elliptic curves over global fields 11G10 Abelian varieties of dimension $$> 1$$ 11G15 Complex multiplication and moduli of abelian varieties 14M17 Homogeneous spaces and generalizations 14K22 Complex multiplication and abelian varieties 14H40 Jacobians, Prym varieties 14G10 Zeta functions and related questions in algebraic geometry (e.g., Birch-Swinnerton-Dyer conjecture)
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### References:

 [1] On the zeta-function of an abelian variety with complex multiplication [2] Publ. Math. Soc. Japan 11 (1971) [3] DOI: 10.2307/1970507 · Zbl 0142.05402 [4] DOI: 10.2969/jmsj/01010001 · Zbl 0081.07603 [5] DOI: 10.1007/BF01361551 · Zbl 0158.08601 [6] DOI: 10.1007/BF01181192 · JFM 54.0405.01 [7] Math. Ann. 97 pp 210– (1926) [8] pp 85– (1953) [9] DOI: 10.1007/BF01594160 · Zbl 0015.40202
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