On the order of vanishing of modular L-functions at the critical point. (English) Zbl 0719.11029

Iwaniec, H.

Sémin. Théor. Nombres Bordx., Sér. II 2, No. 2, 365-376 (1990).

Let \(f(z)=\sum^{\infty}_{n=1}a_ ne^{2\pi inz}\) be a Hecke eigenform, newform of weight 2 for \(\Gamma_ 0(N)\). Its L-series \(L(s)=\sum^{\infty}_{n=1}a_ nn^{-s}\) is also the L-function of an elliptic curve E over \({\mathbb{Q}}\). A condition for the finiteness of the group of rational points of E is \(L'(1,\chi_ d)\neq 0\) for a certain quadratic character \(\chi_ d=(\frac{-d}{y}).\)
In § 2 of [D. Bump, S. Friedberg and J. Hoffstein, Bull. Am. Math. Soc., New Ser. 21, 89-93 (1989; Zbl 0699.10038)] the theorem is announced that \(L'(1,\chi_ d)\neq 0\) holds for infinitely many \(\chi_ d\) associated to imaginary quadratic number fields. Their proof goes along the same lines as in their earlier paper [Ann. Mat., II. Ser. 131, 53-127 (1990; Zbl 0699.10039)]. The same result follows from the main theorem in V. K. Murty [Proc. Conf. on Automorphic Forms and Analytic Number Theory, Montréal, June 1989, 89-113 (1990)].
In the paper under review a more quantitative statement is proved: \(L'(1,\chi_ d)\neq 0\) for at least \(Y^{2/3-\epsilon}\) primitive quadratic characters with \(d<Y\), for Y large enough. This follows from the estimates \[ \sum_{d\leq Y}| L'(1,\chi_ d)|^ 4\ll Y^{2+\epsilon},\quad \sum_{d}L'(1,\chi_ d)F(d/Y)=\alpha_ FY \log Y+\beta_ FY+O(Y^{13/14+\epsilon}) \] with \(\alpha_ F\neq 0\); the test function F is smooth with compact support, and d runs over a set of squarefree numbers.
The proof uses an integral representation for the L-series, the symmetric square L-series associated to f, the large sieve inequality, and other techniques of analytic number theory. It is quite different from the proof of Bump, Friedberg and Hoffstein, which uses automorphic forms more heavily.

Reviewer: R.W.Bruggeman (Utrecht)

MSC:

11F67	Special values of automorphic \(L\)-series, periods of automorphic forms, cohomology, modular symbols
11F11	Holomorphic modular forms of integral weight
11F66	Langlands \(L\)-functions; one variable Dirichlet series and functional equations
11G05	Elliptic curves over global fields
11M41	Other Dirichlet series and zeta functions
11N36	Applications of sieve methods

Keywords:

twisted L-function; vanishing theorem; cusp form; elliptic curve; integral representation for the L-series; symmetric square L-series; large sieve inequality

Citations:

Zbl 0699.10038; Zbl 0699.10039

References:

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