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An automorphic form is a well-behaved function from a topological group $G$ to the complex numbers (or complex vector space) which is invariant under the action of a discrete subgroup $\Gamma \subset G$ of the topological group. Automorphic forms are a generalization of the idea of periodic functions in Euclidean space to general topological groups.

8 votes
1 answer
315 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-S …
Desiderius Severus's user avatar
6 votes
1 answer
212 views

What is the conductor of an automorphic representation for $\Gamma_0(q)$ in $GSp(4)$?

Let $\pi$ be a generic cuspidal automorphic representation on $GSp(4)$, with level $\Gamma_0(q)$ (the group of symplectic matrices with lower left block divisible by $q$), i.e. $$\Gamma_0(q) = \left\{ …
Desiderius Severus's user avatar
9 votes
0 answers
210 views

Why and how is a representation "continuously decomposable"?

What I am asking may apply to a much more general setting and I am interested in the underlying level of generality of these statements, mostly with canonical references. However I state the question …
Desiderius Severus's user avatar
8 votes
0 answers
450 views

Formal degree of discrete series representations

Let $G$ be a locally compact unimodular group. A continuous irreducible unitary representation $\pi$ of $G$ is said to be a discrete series if its matrix coefficients (defined by $\xi^\pi_{v,w} : g \m …
Desiderius Severus's user avatar
9 votes
1 answer
375 views

Relation between $\xi$-cohomological and discrete series

Sometimes, results on automorphic representations are available only under local assumptions. Typically, one could require the representation to be a $\xi$-cohomological cuspidal representation, and I …
Desiderius Severus's user avatar
14 votes
1 answer
522 views

Bound for $GL(3)$ symmetric square

Let $\pi$ be an automorphic representation of $GL(3)$ over a number field. Let $a_n$ be the coefficients of $L(s, \pi, \mathrm{sym}^2)$. Do we know if $$\sum_{n>0} \frac{|a_n|}{n^s}$$ and $$\sum_{n>0} …
Desiderius Severus's user avatar
7 votes
0 answers
135 views

Computing explicit matrix coefficients

I would like to understand in a more explicit way the Fell topology on unitary duals, that is to say the convergence of matrix coefficients of local representations. If I consider a local representati …
Desiderius Severus's user avatar
8 votes
1 answer
461 views

Equivalence between Ramanujan and Selberg conjectures

At first the Ramanujan conjecture for automorphic forms and the Selberg conjecture appear to be understood as totally independent. However, they are now known to be tighyly connected once viewed in th …
Desiderius Severus's user avatar
3 votes
2 answers
245 views

Compactness of the automorphic quotient and genericity

Let $G$ be a reductive group defined over a field $F$. Let $\mathbf{A}$ denote the ring of adeles of $F$. My question is: Assuming the automorphic quotient $[G]=G(F) \backslash G(\mathbf{A})$ is c …
Desiderius Severus's user avatar
8 votes
1 answer
523 views

How strong is the requirement of being a Gelbart-Jacquet lift?

Let $\pi$ be a cuspidal automorphic representation of $\mathrm{GL}(3)$ over a number field $F$. I am wondering how general are Gelbart-Jacquet lifts of automorphic representations of $\mathrm{GL}(2)$ …
Desiderius Severus's user avatar
11 votes
2 answers
1k views

Relation between Fourier coefficients and Satake parameters

Let $L(s)$ be an automorphic L-function (attached to a self contragredient automorphic representation on $GL(3)$), according to the following notations for $s$ of sufficiently large real part: $$L(s) …
Desiderius Severus's user avatar
19 votes
1 answer
908 views

What computer program for automorphic forms

This question has its origins in this entertaining discussion on MO. There are many programs (CAS) and libraries that are able to handle algebraic expressions. These are both a verification tool for …
Desiderius Severus's user avatar
6 votes
1 answer
185 views

Fields of rationality as a notion of automorphic size

I want to interpret the degree of the field of rationality of an automorphic form as a notion of size, analogously to the conductor, and this question is about the possible obstructions to do so. The …
Desiderius Severus's user avatar
2 votes
0 answers
81 views

Continuity of the conductor of automorphic representations

I am interested in properties of (semi-)continuity of the conductor of automorphic representation. Let $F$ be a number field. The meta question is, given a function on the unitary dual of $PGL(2, F)$ …
Desiderius Severus's user avatar
4 votes
1 answer
223 views

Are all these representations supercuspidal

Let $D$ a division quaternion algebra over a number field $F$, and consider $(V,q)$ be a $D$-hermitian space of $D$-dimension $2$, and introduce its group of isometries \begin{align*} \mathrm{GU}(V, q …
Desiderius Severus's user avatar

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