Eigenform

Abstract: The purpose of this article is to show how congruences between the Fourier coefficients of Hecke eigenforms give rise to corresponding congruences between the algebraic parts of the critical values of the associated L-functions. This study was initiated by B. Mazur in his fundamental work on the Eisenstein ideal (see [Maz77] and [Maz79]) where it was made clear that congruences for analytic L-values were closely related to the integral structure of certain Hecke rings and cohomology groups. The results of [Maz79] also showed that congruences were useful in the study of nonvanishing of L-functions. This idea was then further developed by Stevens [Ste82] and Rubin-Wiles [RW82]. The work of Rubin and Wiles, in particular, used congruences to study the behavior of elliptic curves in towers of cyclotomic fields. A key ingredient here was a theorem of Washington, which states, roughly, that almost L-values in certain families are nonzero modulo p. This theme has recently been taken up again, in the work of Ono-Skinner [OSa], [OSb], James [Jam], and Kohnen [Koh97]. While the earlier history was primarily concerned with cyclotomic twists, the current emphasis is on families of twists by quadratic characters. Here one wants quantitative estimates for the number of quadratic twists of a given modular form, which have nonvanishing L-function at s = 1. We continue this trend in the present work by using our general results to obtain a strong nonvanishing theorem for the quadratic twists of modular elliptic curves with rational points of order three. This generalizes a beautiful example due to Kevin James, and provides new evidence for a conjecture of Goldfeld [Gol79]. It should, however, be pointed out that even the study of quadratic twists may be traced back to Mazur: the reader is urged to look at pages 212–213 of [Maz79], and especially at the footnote at the bottom of page 213. The theorems of Davenport-Heilbronn [DH71] and Washington [Was78], which are crucial in this paper, are both mentioned in Mazur’s article. We want to begin by discussing the congruences that lie at the heart of this article. Thus let f = ∑ anq n be an elliptic modular cuspform of level M and weight k ≥ 2. Assume that f is a simultaneous eigenform for all the Hecke operators and that a1(f) = 1. The L-function associated to f is defined by the Dirichlet series L(s, f) = ∑ ann −s, which converges for the real part of s sufficiently large, and has analytic continuation to s ∈ C. A fundamental theorem of Shimura [Shi76] states that L(s, f) enjoys the following algebraicity property:

Abstract: We prove a Weyl-type subconvexity bound for the central value of the $L$-function of a Hecke-Maass form or a holomorphic Hecke eigenform twisted by a quadratic Dirichlet character, uniform in the archimedean parameter as well as the twisting parameter. A similar hybrid bound holds for quadratic Dirichlet $L$-functions, improving on a result of Heath-Brown. As a consequence of these new bounds, we obtain explicit estimates for the number of Heegner points of large odd discriminant in shrinking sets.

Abstract: Fix a prime p, and a modular residual representation ρ : GQ → GL2(Fp). Suppose f is a normalized cuspidal Hecke eigenform of some level N and weight k that gives rise to ρ, and let Kf denote the extension of Qp generated by the q-expansion coefficients an(f) of f . The field Kf is a finite extension of Qp. What can one say about the extension Kf/Qp? Buzzard [1] has made the following conjecture: if N is fixed, and k is allowed to vary, then the degree [Kf : Qp] is bounded independently of k. Little progress has been made on this conjecture so far; indeed, very little seems to have been proven at all regarding the degrees [Kf : Qp]. The goal of this paper is to consider a question somewhat orthogonal to that of Buzzard, namely, to fix the weight and vary the level. Moreover, we only consider certain reducible representations ρ that arise in Mazur’s study of the Eisenstein Ideal [7]. Our results suggest that the degrees [Kf : Qp] are, in fact, arithmetically significant. Suppose that N ≥ 5 is prime, and that p is a prime which exactly divides the numerator of (N−1)/12. Mazur ([7], Prop. 9.6, p. 96 and Prop. 19.1, p. 140) has shown that there is a weight two normalized cuspidal Hecke eigenform defined over Qp, unique up to conjugation by GQp (the Galois group of Qp over Qp), satisfying the congruence a`(f) ≡ 1 + ` mod p (1)

Abstract: We prove integrality of the ratiof, f� /� g, g� (outside an explicit finite set of primes), where g is an arithmetically normalized holomorphic newform on a Shimura curve, f is a normalized Hecke eigenform on GL(2) with the same Hecke eigenvalues as g and � , � denotes the Petersson inner product. The primes dividing this ratio are shown to be closely related to certain level-lowering con- gruences satisfied by f and to the central values of a family of Rankin-Selberg L-functions. Finally we give two applications, the first to proving the integral- ity of a certain triple product L-value and the second to the computation of the Faltings height of Jacobians of Shimura curves.