Skip to main content

All Questions

Filter by
Sorted by
Tagged with
38 votes
4 answers
6k views

Modular forms and the Riemann Hypothesis

Is there any statement directly about modular forms that is equivalent to the Riemann Hypothesis for L-functions? What I'm thinking of is this: under the Mellin transform, the Riemann zeta function $...
Anonymous's user avatar
  • 889
30 votes
2 answers
9k views

Why Is $e^{\pi\sqrt{232}}$ an Almost Integer?

We have already discussed why $e^{(\pi\sqrt{163})}$ is an almost integer. Why are powers of $\exp(\pi\sqrt{163})$ almost integers? Basically $j(\frac{1+\sqrt{-163}}{2} ) \simeq 744 - e^{\pi\sqrt{163}...
Steven Heston's user avatar
28 votes
1 answer
2k views

Intuitive reason why the $j$-invariant is a cube?

Let $\tau$ be a CM point of discriminant $D$. Assume that $D$ is not divisible by $3$. Then $j(\tau)$ is an algebraic integer of degree equal to the class number $h(D)$. Let $ \gamma_2(\tau)=j(\tau)^{...
Shimrod's user avatar
  • 2,375
27 votes
4 answers
2k views

Which quaternary quadratic form represents $n$ the greatest number of times?

Let $Q$ be a four-variable positive-definite quadratic form with integer coefficients and let $r_{Q}(n)$ be the number of representations of $n$ by $Q$. The theory of modular forms explains how $r_{Q}(...
Jeremy Rouse's user avatar
  • 20.4k
23 votes
3 answers
2k views

Why are values of Eisenstein $E_2^*$ algebraic integers?

I'm looking for a proof that the following term is an algebraic integer whenever $\tau_N=\frac{N+\sqrt{-N}}{2}$ is a quadratic irrationality with class number $1$: $$A_N:=\sqrt{-N}\cdot\frac{E_2(\...
L. Milla's user avatar
  • 598
21 votes
1 answer
1k views

Why does this quasi-modular function have integral values?

It is a well-known result that the modular function $1728J(\tau) := \frac{1728E_4(\tau)^3}{E_4(\tau)^3-E_6(\tau)^2}$ has integral values if $\tau$ has class number 1 - for example at $\tau_{163}:=\...
L. Milla's user avatar
  • 598
17 votes
1 answer
987 views

Theta functions, re-expressed

Recall the classical $\theta(q):=\prod_{k=1}^{\infty}(1-q^k)$ and define the sequences $a_n$ and $b_n$ by $$\frac{\theta^3(q)}{\theta(q^3)}=\sum_{n=0}^{\infty}a_nq^n \qquad \text{and} \qquad F(q):=\...
T. Amdeberhan's user avatar
17 votes
2 answers
4k views

On Siegel mass formula

I have asked this question exactly here. The question is as follows: I am interested deeply in the following problem: Let $f$ be a (fixed) positive definite quadratic form; and let $n$ be an ...
Davood Khajehpour's user avatar
15 votes
3 answers
1k views

There is no lattice in PSL(2,R) which contains PSL(2,Z) properly?

How can I see that there is no lattice in $G=\mathrm{PSL}_2( \mathbb{R})$ which contains $\Gamma_1=\mathrm{PSL}_2( \mathbb{Z})$ properly, or equivalently, that $X_1 =\mathrm{PSL}_2(\mathbb{Z}) \...
Marc Palm's user avatar
  • 11.2k
15 votes
5 answers
2k views

Very strong multiplicity one for Hecke eigenforms

In Invent. math. 116, 645-649 (1994) Dinakar Ramakrishnan proves a theorem which I understand to imply that the following statement (in light of the fact that elliptic curves over $\mathbb{Q}$ are ...
Jonah Sinick's user avatar
  • 7,062
15 votes
1 answer
680 views

Is $\eta(\tau)^2$ a modular form of weight 1 on $\Gamma(12)$?

As we know, the Dedekind eta function $\eta(\tau)$ acquires a phase $\exp(2\pi i/24)$ under the modular transformation: $\tau \rightarrow \tau+1$. Therefore $\eta(\tau)^2$ is invariant under $\tau \...
Franklin Wu's user avatar
14 votes
4 answers
3k views

Jacobi's theorem on sums of two squares (reference request)

One of Jacobi's theorems states that the number of representations of a positive integer $n$ as a sum of two squares of integers equals $$4(d_1(n)-d_3(n)),$$ where the function $d_i$ counts the number ...
Dr. Pi's user avatar
  • 3,062
13 votes
3 answers
2k views

Density of a set of integers

EDIT: this question of mine has received little attention, perhaps in part because it was stated in a too general and complicated way. So let me give it a second chance: Fix an integer $r \geq 0$. ...
Joël's user avatar
  • 26k
12 votes
3 answers
2k views

Kronecker's Jugendtraum for real quadratic fields?

Kronecker's Jugendtraum (or Hilbert's 12'th problem) is to find abelian extensions of arbitrary number fields by adjoining `special' values of transcendental functions. The Kronecker-Weber theorem was ...
Adam Harris's user avatar
  • 1,905
12 votes
1 answer
997 views

How much can an Eisenstein series be truncated?

For ease of exposition, I will stick to the simplest case: consider the Eisenstein series for $SL_2(\bf R)$ $$E(z,s)=\sum_{\gamma\in P_{\bf Z}\backslash SL_2(\bf Z)}\text{Im}(\gamma z)^s=\sum_{(c,d)\...
Tian An's user avatar
  • 3,799
12 votes
0 answers
508 views

Weyl law for Maass forms with nontrivial character

The classical Weyl law for $\Gamma = \mathrm{SL}_2(\mathbb{Z})$ counts the number of Maass cusp forms on $\Gamma \backslash \mathbb{H}$ with Laplace eigenvalue less than $T$. This is originally due to ...
Peter Humphries's user avatar
11 votes
2 answers
551 views

Effective bound on the expansion of the $j$-invariant

The $j$-ivariant has the following Fourier expansion $$j(\tau)=\frac 1q +\sum_{n=0}^{\infty}a_nq^n=\frac{1}{q}+744+196884q+21493760q^2+\cdots.$$ Here is $q=e^{2\pi i \tau}$. Is there some simple ...
Shimrod's user avatar
  • 2,375
11 votes
1 answer
699 views

"strange" diophantine and parity of the partition function

Let $\{x_i\}:=\{x_1=5, x_2=13, x_3=29, x_4=37, x_5=45, \dots \}$ be the sequence of those positive integers of the form $$ p^{4\alpha+1}n^2$$ in increasing order where $p\equiv 5\pmod 8$ is prime ...
T. Amdeberhan's user avatar
11 votes
1 answer
563 views

Is $j(\tau)^{1/3}$ the hauptmodul for the congruence subgroup generated by $\tau\rightarrow\tau+3, \tau\rightarrow-1/\tau$?

The 3rd root of the modular invariant $j$ is $$ j(\tau)^{1/3}=q^{-1/3}(1+ 248q+ 4124q^2+ 34752q^3+\cdots),$$ where $q=e^{2\pi i \tau}$. I was wondering if $j(\tau)^{1/3}$ the hauptmodul for the ...
Franklin Wu's user avatar
11 votes
1 answer
262 views

The best bound on the growth of $\sum_{n\le X}a(n)$

Let $f(z) = \sum_{n=1}^{\infty} a(n)n^{(k-1)/2} q^n$ be a cusp form, I am interested to know what is currently the best bound on the growth of $\sum_{n\le X}a(n)$ in the following two case : When $f$ ...
User 101794987's user avatar
11 votes
1 answer
660 views

What is the motivation behind Ramanujan's conjecture?

One motivation I have seen given for Ramanujan's conjecture for the estimate $$ |a_p|< C p^{k - \frac{1}{2}} $$ for the Fourier coefficients of a cusp form of weight $2k$ is that it allows one to ...
Keivan Karai's user avatar
  • 6,224
10 votes
2 answers
1k views

Modular forms with finitely many or very few non-zero Fourier coefficients

I have an elementary question on modular forms, but which I don't know how to solve. a) Is there a congruence subgroup $\Gamma \leq \mathrm{SL}_2(\Bbb Z)$, an integer $k \in \Bbb Z$ and a non-...
Alphonse's user avatar
  • 255
10 votes
1 answer
716 views

Why are the coefficients of the modular equation so large?

The modular equation $\Phi_n(X,Y)$ is a polynomial in $\mathbf Z[X,Y]$ relating the modular invariant $j$ and the functions $j\left(\frac{a\tau+b}{c\tau+d}\right)$, where $ad-bc=n$. For example, we ...
Shimrod's user avatar
  • 2,375
10 votes
2 answers
705 views

Averages over integer points of the sphere

A paper of William Duke proves that integer points on the sphere are equidistributed: $$ V_n = \{ (x,y,z) \in \mathbb{Z}^2 : x^2 + y^2 + z^2 = n \}. $$ Up to reflections across the $x$, $y$ and $z$ ...
john mangual's user avatar
  • 22.8k
10 votes
1 answer
314 views

Coefficient bounds on cusp forms, half-integer weight

Let $f(\tau) = \sum_{n=1}^{\infty} a(n) q^n$ be a cusp form on $\Gamma_0(4N)$ of half-integer weight $k \ge 5/2.$ The Ramanujan-Petersson conjecture in this case is that $$a(n) \ll n^{(k-1)/2 + \...
user105068's user avatar
10 votes
1 answer
1k views

Reference for the odd dihedral case of Artin's conjecture

The example that Matt Emerton cited here prompted me to become interested in how one proves that odd two dimensional dihedral Galois representation are modular. This is the first case of the strong ...
Jonah Sinick's user avatar
  • 7,062
9 votes
2 answers
556 views

Holomorphic Hoffstein-Lockhart

In the article Hoffstein, Jeffrey; Lockhart, Paul "Coefficients of Maass forms and the Siegel zero." Ann. of Math. (2) 140 (1994), no. 1, 161–181, it is stablished a good bound for the Petersson norm ...
Ricardo Menares's user avatar
9 votes
1 answer
530 views

standard zero free region of automorphic L-function on GL(N)

Let $L(s,\pi)$ be the standard(Godement-Jacquet) $L$-function of $\pi$, where $\pi$ is a cuspidal automorphic represetation of $GL(m,A_Q)$. What's the standard zero-free region for $L(s,\pi)$? any ...
7-adic's user avatar
  • 3,804
9 votes
0 answers
208 views

Unexpected patterns on the graph of an L-function on the critical line

Let $L(s)$ be the $L$-function associated to the (only) classical modular form of weight $26$ and level $1$. The completed L-function $\Lambda(s)=2(2\pi)^{-s}\Gamma(s) L(s)$ is symmetric with respect ...
LeechLattice's user avatar
  • 9,501
9 votes
0 answers
435 views

Rankin-Selberg for Maass form GL(3)xGL(2)

Let $F$ be a Maass cusp form for $\mathrm{SL}(3,\mathbb{Z})$ (level 1 trivial character). Let $g$ be a Maass cusp form for $\Gamma_0(N)$ with character $\chi$ mod $N$. For convenience, you may assume ...
7-adic's user avatar
  • 3,804
8 votes
3 answers
1k views

Effective detection of CM modular forms

Say $f$ is a newform of weight $k$ and level $\Gamma_1(N)$. $f$ is called CM if, for example, there is an imaginary quadratic field $K$ such that for all $p\nmid N$ which are inert in $K$, the $p$th ...
Rob Harron's user avatar
  • 4,807
8 votes
2 answers
744 views

A question related to Hilbert modular form

This is a question related to Hilbert modular forms. Let $\mathbb{K}=\mathbb{Q}(\sqrt D)$ be an imaginary quadratic field with discriminant $D<0$ and $\zeta (\text{mod } m)$ a Hecke character such ...
user15243's user avatar
  • 424
8 votes
1 answer
1k views

Functional equation and conductor for a Rankin-Selberg convolution

Let $f$ be a Modular form/Maass form on $GL(2)$ with level $N$ and character $\eta$ and Fourier coefficients $a(n)$. The Rankin-Selberg convolution $$L(s,f\times\bar f)=\sum \frac{a(n)\overline{a(n)}}...
Jeep Wrangler's user avatar
8 votes
1 answer
739 views

Average of Fourier coefficients of a cusp form of half integral weight

Suppose $f$ is a cusp form of half integral weight $k$ w.r.t. the group $\Gamma_0(4)$ ($k$ is not very low, can assume $k \ge 11/2$), and $a_n$ is its Fourier coefficient. The Linnik bound says that ...
Fan Zheng's user avatar
  • 5,169
8 votes
1 answer
356 views

Average bounds on Rankin-Selberg coefficients for modular forms

Let $f$ be a cuspidal Hecke newform of weight $k$ and level $N$, and denote by $a_f(n)$ its $n$-th Fourier coefficient. The newform $f$ is normalized so that $a_f(1) = 1$. As a consequence of Rankin-...
Desiderius Severus's user avatar
7 votes
1 answer
501 views

Smallest Mazur's good prime

Let $p$ and $\ell$ be primes $\geq 5$ such that $\ell$ divides $p-1$. Following Mazur, we say that a prime $q$ is a $\textit{good prime}$ if $\ell$ does not divide $q-1$ and $q$ is not a $\ell$th ...
Emmanuel Lecouturier's user avatar
7 votes
1 answer
435 views

Fricke involution and Atkin operator

Let $f\in S_k(\Gamma_0(N))$ be a cusp form for $N>1$. Consider the following operators acting on $f$ via the natural action of $GL_2^{+}(\mathbb{R})$ : $$ W_N=\begin{pmatrix} 0 & -1\\ N & 0 ...
Akash Yadav's user avatar
7 votes
2 answers
478 views

Rankin-Selberg integral for GL(3) form with Odd Maass form on GL(2)

Let $F$ be a Hecke-Maass cusp form for $SL_3(\mathbb Z)$. Let $u$ be a Hecke-Maass cusp form for $SL_2(\mathbb Z)$. The following integral $$\mathcal L(s,F\times u)=\int_{{SL}(2,\mathbb{Z})\...
7-adic's user avatar
  • 3,804
7 votes
1 answer
175 views

Is every eigenvector sequence for the Hecke operators a eigenform?

Let $f(n) = a_n$ be a sequence taking values in $\mathbb C$ for $n=1,2,...$. Let $T_m$ be the Hecke operators (of a fixed weight $k$) defined as usual in terms of the $a_n$. That is: $$T_m(f)(n) = \...
Asvin's user avatar
  • 7,746
7 votes
1 answer
489 views

Complete L-function and FE of Rankin-Selberg on GL(2)?

Let $f$ be a Maass cusp form of $\Gamma_0(N)$ on the upper half plane with character $\chi$ mod $N$ and eigenvalue $1/4+\mu^2$. What is the complete $L$-function of the Rankin-Selberg product $L(s,f\...
7-adic's user avatar
  • 3,804
7 votes
1 answer
811 views

Alternative way to prove the functional equation for Eisenstein series?

Let $E(z,s):=\pi^{-s}\Gamma (s) \sum_{(m,n)=1}\frac{y^s}{|mz+n|^{2s}}$ be the real-analytic Eisenstein series. It satisfies the functional equation $E(z,s)=E(z,1-s)$ with two poles at $s=0,1$. The ...
7-adic's user avatar
  • 3,804
7 votes
1 answer
353 views

Numerically double-checking formula with L-values

I'm working with a special case of Ichino's triple product formula, which for classical holomorphic newforms $f$, $g$ ,$h$ of weights $k$, $m-k$, $m$ (and central characters satisfying $\chi_f \chi_g =...
Dan Collins's user avatar
7 votes
1 answer
264 views

Upper bound of the analytic rank of the modular Jacobian varieties $J_1(N)$

Does there exist an upper bound of the analytic rank of the modular Jacobian varieties $J_1(N)$? (Or more generally of $J_\Gamma$ for a congruence subgroup $\Gamma_0 \subseteq \Gamma \subseteq \...
k.j.'s user avatar
  • 1,364
7 votes
0 answers
673 views

Mock modular forms and (indefinite) quadratic forms

Define the function $$f(q,z,y) = \sum_{n \ge 0,m,l} c(n,m,l) q^n z^m y^l$$ where $c(n,m,l)$ is defined by $$ c(n,m,l) = \begin{cases} (-1)^{s+l} & \text{if } 4n - m^2 + l^2 = 2s(s+1)\\ 0 & \...
Richard Eager's user avatar
6 votes
1 answer
305 views

Are the Fourier coefficients of $\eta(q^m)^m / \eta(q)$ non-negative?

In this paper, the following result is proved. For any prime $p$, all the Fourier coefficients of $$\eta(q^p)^p / \eta(q) = q^{\frac{p^2-1}{12}} \prod_{n=1}^\infty (1 - q^{pn})^p (1 - q^{n})^{-1}$$ ...
TOM's user avatar
  • 427
6 votes
1 answer
943 views

Voronoi formula for the symmetric $L$-function with level $N $

Sorry to disturb. Does any experts here know something upon the Voronoi type for the symmetric $L$-functions$$\sum_{n\le X} A_F(1,n)e\left ( \frac{an}{c}\right)=?$$ Here $F$ is a symmetric-lift of a $...
FeiHou's user avatar
  • 353
6 votes
1 answer
2k views

The connection between the Weil conjectures and Ramanujan's conjecture

I'm writing an essay about Ramanujan's conjecture and have some questions: 1 How is Ramanujan's conjecture connected with the Weil conjectures? 2 How could Ramanujan's conjecture be assumed true or ...
user avatar
6 votes
1 answer
600 views

How to compute Coefficients in Chudnovsky's Formula?

My aim is to understand all three coefficients arising in the Chudnovsky-Formula (see also Question 300385). Two of them are easily computed, but I failed with the third: It is known that for all $\...
L. Milla's user avatar
  • 598
6 votes
2 answers
392 views

A lower-bound for the square-mean of Fourier coefficients of cusp forms at primes argument

There is a basis question which puzzles me for a while. The question is the following: Let $X\ge 2,$ and $\lambda(n)$ be the $n$-th Fourier coefficient of a $GL(2)$ newform of prime level $N>1$, ...
hofnumber's user avatar
  • 563
6 votes
1 answer
678 views

Root number of the Rankin-Selberg convolution of two newforms

Let $p$ and $q$ be two distinct primes. Let $f\in \mathcal{S}_k^{\ast}(pq,\psi)$ be a holomorphic newform of level $pq$, nebentypus $\psi$, and weight $k$, where $\psi = \chi_p \chi_{0(q)}$, with $\...
lin's user avatar
  • 63