Yujiao Jiang, Yuk-Kam Lau, Guangshi Lü, Emmanuel Royer, Jie Wu
In this paper, we investigate the sign changes of Fourier coefficients of half-integral weight Hecke eigenforms and give two quantitative results on the number of sign changes.
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We survey divisibility properties of the Fourier coefficients of modular functions inspired by Ramanujan. Then using recent results of the generalized Hecke operator on harmonic Maass functions and known divisibility of Fourier coefficients of modular functions, we establish congruence relations of the Fourier coefficients of certain modular functions and mock modular functions of various levles.
The goal of this paper is to improve existing bounds for Fourier coefficients of higher genus Siegel modular forms of small weight.
We establish (Theorem 3.6) polynomial-growth estimates for the Fourier coefficients of holomorphic logarithmic vector-valued modular forms.
New bounds for fundamental Fourier coefficients of Siegel modular forms
该研究运用Iwaniec方法得到Jacobi形式Fourier系数的新界，并结合二次Siegel模形式的Fourier-Jacobi展开，推导出Siegel模形式基本Fourier系数的强上界。
We study several aspects of nonvanishing Fourier coefficients of elliptic modular forms $\bmod \ell$, partially answering a question of Bellaïche-Soundararajan concerning the asymptotic formula for the count of the number of Fourier coefficients upto $x$ which do not vanish $\bmod \ell$. We also propose a precise conjecture as a possible answer to this question. Further, we prove several results related to the nonvanishing of arithmetically interesting (e.g., primitive or fundamental) Fourier coefficients $\bmod \ell $ of a Siegel modular form with integral algebraic Fourier coefficients provi…
We describe the $p$-divisibility transposition for the Fourier coefficients of Siegel modular forms. This provides a supplement to the result by Wilton for $p$-divisibility satisfied by the Ramanujan $τ$-function.
On p-divisibility of Fourier coefficients of Hermitian modular forms
本文研究 Hermitian 模形式 Fourier 系数的 p-可整除性换位，并证明其呈现与 Siegel 模形式相同的现象。
Sign patterns of Fourier coefficients of modular forms
研究模形式傅里叶系数符号对确定性的影响，提出通过符号条件确定模形式的条件。
We prove the following theorem. Suppose that $F=(f_1, f_2)$ is a 2-dimensional vector-valued modular form on $SL_2(Z)$ whose component functions $f_1, f_2$ have rational Fourier coefficients with bounded denominators. Then $f_1$ and $f_2$ are classical modular forms on a congruence subgroup of the modular group.
We generalize Merel's work on universal Fourier expansions to Bianchi modular forms over Euclidean imaginary quadratic fields, under the assumption of the nondegeneracy of a pairing between Bianchi modular forms and Bianchi modular symbols. Among the key inputs is a computation of the action of Hecke operators on Manin symbols, and building upon the Heilbronn-Merel matrices constructed by Mohamed.
The aim of this article is to study the fields generated by the Fourier coefficients of Hilbert newforms at arbitrary cusps. Precisely, given a cuspidal Hilbert newform $f$ and a matrix $σ$ in (a suitable conjugate of) the Hilbert modular group, we give a cyclotomic extension of the field generated by the Fourier coefficients at infinity which contains all the Fourier coefficients of $f||_kσ$.
Bounds for Moments of Twisted Fourier coefficients of Modular Forms
本文在广义黎曼假设下，为模L函数的移位矩及二次扭矩建立上界，并据此推导出模形式傅里叶系数与狄利克雷字符扭和之矩的界。
We establish lower bounds for (i) the numbers of positive and negative terms and (ii) the number of sign changes in the sequence of Fourier coefficients at squarefree integers of a half-integral weight modular Hecke eigenform.
We discuss the approximation of real numbers by Fourier coefficients of newforms, following recent work of Alkan, Ford and Zaharescu. The main tools used here, besides the (now proved) Sato-Tate Conjecture, come from metric number theory.
Let $ρ: SL(2,\mathbb{Z})\to GL(2,\mathbb{C})$ be an irreducible representation of the modular group such that $ρ(T)$ has finite order $N$. We study holomorphic vector-valued modular forms $F(τ)$ of integral weight associated to $ρ$ which have \emph{rational} Fourier coefficients. (These span the complex space of all integral weight vector-valued modular forms associated to $ρ$.) As a special case of the main Theorem, we prove that if $N$ does \emph{not} divide 120 then every nonzero $F(τ)$ has Fourier coefficients with \emph{unbounded denominators}.
In this note, we explicitly construct mock modular forms with integral Fourier coefficients by evaluating regularized Petersson inner products involving their shadows, which are unary theta functions of weights 1/2 and 3/2 . In addition, we also improve the known bounds for the denominators of the coefficients of mock modular forms whose shadows are holomorphic weight one cusp forms constructed by Hecke.
We investigate integrality and divisibility properties of Fourier coefficients of meromorphic modular forms of weight $2k$ associated to positive definite integral binary quadratic forms. For example, we show that if there are no non-trivial cusp forms of weight $2k$, then the $n$-th coefficients of these meromorphic modular forms are divisible by $n^{k-1}$ for every natural number $n$. Moreover, we prove that their coefficients are non-vanishing and have either constant or alternating signs. Finally, we obtain a relation between the Fourier coefficients of meromorphic modular forms, the coeff…
In this article, we give some results on simultaneous non-vanishing and simultaneous sign-changes for the Fourier coefficients of two modular forms. More precisely, given two modular forms $f$ and $g$ with Fourier coefficients $a_n$ and $b_n$ respectively, we consider the following questions: existence of infinitely many primes $p$ such that $a_p b_p\neq 0$; simultaneous non-vanishing in the short intervals and in arithmetic progressions; simultaneous sign changes in short intervals.
On the Divisibility Properties of the Fourier Coefficients of Meromorphic Hilbert Modular Forms
本研究沿用Zagier的思路，借助theta提升与弱Maass形式，探究实二次域对应的亚纯希尔伯特模形式傅里叶系数的有理性和整除性，给出系数为分母有界有理数的条件，并证明其在合适线性组合下的整除特性。
In this note, we show that the algebraicity of the Fourier coefficients of half-integral weight modular forms can be determined by checking the algebraicity of the first few of them. We also give a necessary and sufficient condition for a half-integral weight modular form to be in Kohnen's +-subspace by considering only finitely many terms.
This article is concerned with the Fourier coefficients of cusp forms (not necessarily eigenforms) of half-integer weight lying in the plus space. We give a soft proof that there are infinitely many fundamental discriminants $D$ such that the Fourier coefficients evaluated at $|D|$ are non-zero. By adapting the resonance method, we also demonstrate that such Fourier coefficients must take quite large values.
We determine the structure over $\mathbb{Z}$ of the ring of symmetric Hermitian modular forms with respect to $\mathbb{Q}(\sqrt{-1})$ of degree $2$ (with a character), whose Fourier coefficients are integers. Namely, we give a set of generators consisting of $24$ modular forms. As an application of our structure theorem, we give the Sturm bounds of such the modular forms of weight $k$ with $4\mid k$, in the case $p=2$, $3$. We remark that the bounds for $p\ge 5$ are already known.
Let $d(n)$ denote the number of divisors of $n$. In this paper, we study the average value of $d(a(p))$, where $p$ is a prime and $a(p)$ is the $p$-th Fourier coefficient of a normalized Hecke eigenform of weight $k \ge 2$ for $Γ_0(N)$ having rational integer Fourier coefficients.
A thorough analysis is made of the Fourier coefficients for vector-valued modular forms associated to three-dimensional irreducible representations of the modular group. In particular, the following statement is verified for all but a finite number of equivalence classes: if a vector-valued modular form associated to such a representation has rational Fourier coefficients, then these coefficients have "unbounded denominators", i.e. there is a prime number p, depending on the representation, which occurs to an arbitrarily high power in the denominators of the coefficients. This provides a verif…
Bounds for integral moments of quadratic twists of Fourier coefficients of modular forms
本文在广义黎曼猜想下给出模形式傅里叶系数二次扭特征和的积分矩上界，并证明其最优性。
We prove a formula of Petersson's type for Fourier coefficients of Siegel cusp forms of degree 2 with respect to congruence subgroups, and as a corollary, show upper bound estimates of individual Fourier coefficient. The method in this paper is essentially a generalization of Kitaoka's previous work which studied the full modular case, but some modification is necessary to obtain estimates which are sharp with respect to the level aspect.
Divisor problems for restricted Fourier coefficients of modular forms
研究模形式的傅里叶系数的除数函数平均值，探讨整数次幂下的平均行为及角度约束条件下的贡献。
In this article, we study the simultaneous sign changes of the Fourier coefficients of two Hilbert cusp forms of different integral weights. We also study the simultaneous non-vanishing of Fourier coefficients, of two distinct non-zero primitive Hilbert cuspidal non-CM eigenforms of integral weights, at powers of a fixed prime ideal.
In this paper, we investigate Fourier expansions of meromorphic modular forms. Over the years, a number of special cases of meromorphic modular forms were shown to have Fourier expansions closely resembling the expansion of the reciprocal of the weight $6$ Eisenstein series which was computed by Hardy and Ramanujan. By investigating meromorphic modular forms within a larger space of so-called polar harmonic Maass forms, we prove in this paper that all negative-weight meromorphic modular forms (and furthermore all quasi-meromorpic modular forms) have Fourier expansions of this type, granted tha…
We prove a non-vanishing result of modular L-values with quadratic twists, where the quadratic discriminants are in a short interval. Using this fact and Waldspurger's theorem, we improve the results of Balog-Ono[The chebotarev density theorem in short intervals and some questions of Serre, Journal of number theory. 91(2):356-371(2001)] on the non-vanishing of Fourier coefficients of half-integral weight eigenform.
We show that the Dirichlet series associated to the Fourier coefficients of a half-integral weight Hecke eigenform at squarefree integers extends analytically to a holomorphic function in the half-plane $\re s\textgreater{}\tfrac{1}{2}$. This exhibits a high fluctuation of the coefficients at squarefree integers.
Fourier Coefficients of Weight Zero Mixed False Modular Forms
本文利用并推广圆法及Bringmann、Nazaroglu、Rademacher的技巧，结合Kloosterman和的模$k$上界，给出无穷族权零混合假模形式傅里叶系数的精确公式。
Mean squares of quadratic twists of the Fourier coefficients of modular forms
本文渐近求值了给定模形式傅里叶系数在二次扭曲下的平滑求和版本，涉及Kronecker符号及正奇无平方整数求和。
Low moments of random multiplicative functions twisted by Fourier coefficients of modular forms
研究随机乘法函数与模形式傅里叶系数的矩性质，确定在特定范围内的矩阶大小。
The Fourier coefficients and singular moduli of the elliptic modular function $j(τ)$, revisited
本文综述了将椭圆模$j$函数傅里叶系数表示为奇异模有限和的Kaneko公式自1996年提出后，在联系模形式傅里叶系数与模函数特殊值的框架下的多方向后续发展。
Let F be a Siegel cusp form of weight k and genus n>1 with Fourier-Jacobi coefficients f_m. In this article, we estimate the growth of the Petersson norms of f_m, where m runs over an arithmetic progression. This result sharpens a recent result of Kohnen in [5].
Fourier coefficients and cuspidality of modular forms: a new approach
本文通过新的归纳方法区分模形式的cuspidal形式，确定了最佳权重范围，并探讨了通过Jacobi-傅里叶系数反推cuspidality的可能性。
This article is a research exposition based on the author's talk at the International Colloquium on Automorphic Representations and L-Functions, 2012, held at TIFR, Mumbai. We consider some special cases of the following question: when is a natural subset of the Fourier coefficients sufficient to uniquely determine a "modular form"? Two kinds of modular forms are considered in this article: a) classical modular forms of half-integral weight, and b) Siegel modular forms of genus 2 and integral weight. These two apparently different scenarios turn out to be closely related. Our results were moti…
An alternative proof of the asymptotic formula for the Fourier coefficients of the elliptic modular $j$-function
本文基于概率方法，利用具有简单无穷乘积的模函数表示，证明了椭圆模 $j$-函数系数的渐近公式。
We study the probabilistic behavior of sums of Fourier coefficients in arithmetic progressions. We prove a result analogous to previous work of Fouvry-Ganguly-Kowalski-Michel and Kowalski-Ricotta in the context of half-integral weight holomorphic cusp forms and for prime power modulus. We actually show that these sums follow in a suitable range a mixed Gaussian distribution which comes from the asymptotic mixed distribution of Salié sums.
Automatic convergence and arithmeticity of modular forms on exceptional groups
本研究证明F₄与Eₙ型群上尖点四元数模形式空间具纯代数刻画，核心是证明相关无穷和绝对收敛，进而推出其存在傅里叶系数全为代数数的基，推动了例外群上模形式的算术性质研究。
Modular Forms with Only Nonnegative Coefficients
研究SL₂(Z)上无负傅里叶系数的模形式，确定非负性Sturm界A(k)的上下界及傅里叶系数上界。
We correct a mistake in \cite{St} leading to erroneous formulas in Theorems 5.2 and 5.4. As an immediate corollary of a formula in \cite{BCJ} we give a formula, which relates the Hecke operators $T(p^2)\circ T(p^{2l-2})$, $T(p^{2l})$ and $T(p^{2l-4})$ and comment on it.
Distribution of local signs of modular forms and murmurations of Fourier coefficients
该研究在模形式领域，证明了局部根数的相关符号偏向结果，提出更一般局部根数组合下的murmurations现象猜想，并修正了过往合著论文的符号错误。
We study sums of additively twisted Fourier coefficients of a holomorphic cusp form, a Maass cusp form, and the symmetric-square lift of a holomorphic cusp form. We obtain bounds that are uniform with respect to both the form and the terms of the additive twist. We also improve a bound on a sum of additively twisted Fourier coefficients of a holomorphic cusp form that have also been twisted by a nonlinear exponential term. This last bound is uniform with respect to the terms of the additive twist but it is not uniform with respect to the form.
In this note, we generalize the isomorphisms to the case when the discriminant form is not necessarily induced from real quadratic fields. In particular, this general setting includes all the subspaces with epsilon-conditions, only two spacial cases of which were treated before. With this established, we shall prove the Zagier duality for canonical bases. Finally, we raise a question on the integrality of the Fourier coefficients of these bases elements, or equivalently we concern the existence of a Miller-like basis for vector valued modular forms.
Let $f$ be a half-integral weight cusp form of level $4N$ for odd and squarefree $N$ and let $a(n)$ denote its $n^{\rm th}$ normalized Fourier coefficient. Assuming that all the coefficients $a(n)$ are real, we study the sign of $a(n)$ when $n$ runs through an arithmetic progression. As a consequence, we establish a lower bound for the number of integers $n\le x$ such that $a(n)>n^{-α}$ where $x$ and $α$ are positive and $f$ is not necessarily a Hecke eigenform.
Let $f\in S_{k+1/2}(N,χ)$ be a Hecke eigenform of half integral weight $k+1/2\,(k\geq 2)$ and the real nebentypus $χ=\pm 1$ where the Fourier coefficients $a(n)$ are reals. We prove that the sequence $\{χ(p^ν)a(tp^{2ν})\}_{ν\in\N}$ has infinitely many sign changes for almost all primes $p$ where $t$ is a squarefree integer such that $a(t)\neq 0$. The same result holds for the sequences of Fourier coefficients $\{a(tp^{2(2ν+1)})\}_{ν\in\N}$ and $\{a(tp^{4ν})\}_{ν\in\N}$.
The shifted convolution problem for Fourier coefficients of Siegel modular forms of degree $2$
本文提出了一种基于自守诠释的新方法，首次对更高秩群上的移位卷积和给出了非平凡估计，通过估计塞尔曼泊松级数的傅里叶系数实现。
Associated to an (adelic) Hilbert modular form is a sequence of `Fourier coefficients' which uniquely determine the form. In this paper we characterize Hilbert modular cusp forms by the size of their Fourier coefficients. This answers in the affirmative a question posed by Winfried Kohnen.
We prove that if $F$ is a non-zero (possibly non-cuspidal) vector-valued Siegel modular form of any degree, then it has infinitely many non-zero Fourier coefficients which are indexed by half-integral matrices having odd, square-free (and thus fundamental) discriminant. The proof uses an induction argument in the setting of vector-valued modular forms. In an Appendix, as an application of a variant of our result and building upon the work of A. Pollack, we show how to obtain an unconditional proof of the functional equation of the spinor $L$-function of a holomorphic cuspidal Siegel eigenform …
Lower Bounds on High Moments of Twisted Fourier coefficients of Modular Forms
本文研究了模形式扭曲Fourier系数的高次矩问题，针对大素数q和实数k≥2，证明了2k次矩的下界，并在广义Riemann假设下证明了该界在常数因子范围内是精确的。
Graded Algebras of Modular Forms and Sign Changes of Fourier Coefficients for Eta Quotients
本文确定了N=8,12,16,20,32时模形式分次代数的显式结构，给出eta商生成元与关系，并利用eta商基得到三个特定空间中傅里叶系数符号周期性的充要条件，最终找出所有符号周期性的eta商。
On the Vanishing and Cuspidality of $D_4$ Modular Forms
本文研究了 $D_4$ 模形式的消失与 cuspidality 性质，通过标量傅里叶系数理论发展了判据，并刻画了 Pollack 的四元数 Saito-Kurokawa 子空间。
Divisor moments of polynomials in Fourier coefficients of modular forms
研究非CM新形式傅里叶系数多项式表达式上除数函数高阶矩，证明中对数指数取决于多项式不可约因子数且在佐藤-泰特限制下不变，结合多种定理及算术、均值估计得出结论。
Modular forms with non-vanishing central values and linear independence of Fourier coefficients
本文通过将VanderKam定理推广到高权模符号，证明对大素数p及D²≪p，Hecke算子T₁,…,T_D在权2k尖点模符号空间的winding元素上线性无关，从而给出中心临界值非零的新形式数量界及其模l约化的线性无关性。
We show that the values of a certain family of weakly holomorphic modular functions at points in the divisors of any meromorphic modular form with algebraic Fourier coefficients are algebraic. We use this to extend the classical result of Schneider by proving that zeros or poles of any non-zero meromorphic modular form with algebraic Fourier coefficients are either transcendental or imaginary quadratic irrational.
Throughout the 1980's, Kudla and the second named author studied integral transforms from rapidly decreasing closed differential forms on arithmetic quotients of the symmetric spaces of orthogonal and unitary groups to spaces of classical Siegel and Hermitian modular forms. These transforms came from the theory of dual reductive pairs and the theta correspondence. They computed the Fourier expansion of these transforms in terms of periods over certain totally geodesic cycles . This also gave rise to the realization of intersection numbers of these `special' cycles with cycles with compact supp…
Recently, Bruinier and Ono classified cusp forms $f(z) := \sum_{n=0}^{\infty} a_f(n)q ^n \in S_{λ+1/2}(Γ_0(N),χ)\cap \mathbb{Z}[[q]]$ that does not satisfy a certain distribution property for modulo odd primes $p$. In this paper, using Rankin-Cohen Bracket, we extend this result to modular forms of half integral weight for primes $p \geq 5$. As applications of our main theorem we derive distribution properties, for modulo primes $p\geq5$, of traces of singular moduli and Hurwitz class number. We also study an analogue of Newman's conjecture for overpartitions.
We show, for levels of the form $N = p^a q^b N'$ with $N'$ squarefree, that in weights $k \geq 4$ every cusp form $f \in \mathcal{S}_k(N)$ is a linear combination of products of certain Eisenstein series of lower weight. In weight $k=2$ we show that the forms $f$ which can be obtained in this way are precisely those in the subspace generated by eigenforms $g$ with $L(g, 1) \neq 0$. As an application of such representations of modular forms we can calculate Fourier expansions of modular forms at arbitrary cusps and we give several examples of such expansions in the last section.
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