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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.

4 votes

Conductor of monomial forms with trivial nebentypus

Just to augment Kevin's series of comments: I think that the conductor of the induction of some character $\chi$ over a quadratic field to $\mathbb Q$ would normally equal $D N(C)^2$, where $D$ is the …
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6 votes

Is there a canonical notion of "mod-l automorphic representation"?

If $G$ is a connected, linear, reductive group over $\mathbb Q$, let $q_0$ be the dimension so denoted in Borel--Wallach, i.e. $q_0 = (d - l_0)/2,$ where $d = \text{dim } G_{\infty} - \text{ dim } A_ …
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3 votes
Accepted

extending cusp forms

I believe the answer should be yes, by some version of the following sketch of an argument: (Note: by restriction of scalars, I regard all groups as being defined over $\mathbb Q$, and I write ${\mat …
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11 votes
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Local to Global principle for reductive groups

If $\pi_v$ is supercuspidal, then (after making a twist if necessary) it should be possible to find an automorphic $\pi$ with $\pi_v$ as the local factor at $v$. This kind of result is usually proved …
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6 votes
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Automorphic forms and Galois representations over imaginary quadratic fields: generalizing T...

Various groups of people have thought about/are thinking about this. The natural source of the desired Galois reps. is a $U(2,2)$ Shimura variety. The problem is that the cohomology of this variety …
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11 votes
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strong approximation and one-dimensional automorphic representations

Let $G$ be the group of norm one elements in $D^{\times}$. An easy argument shows that it suffices to prove the claim for $G$ in place of $D^{\times}$. In other words, I will let $\pi$ be an automorp …
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8 votes

embedding of local tempered representation into cuspidal automorphic representation

As Joel points out, this is not possible. Even in the case of a discrete series rep'n, one can't control the value of the central character on the non-compact part of $F_v^*$. What one can do (in so …
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23 votes
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What is the current status of the function fields Langlands conjectures?

(1) Regarding the relationship between geometric Langlands and function field Langlands: typically research in geometric Langlands takes place in the context of rather restricted ramification (everywh …
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16 votes
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Why isn't meromorphic continuation enough for converse theorems?

Dear Kevin, My understanding of the current meromorphic continuation results is that they do something along the lines of expressing a given Galois representation as the induction of a virtual (i.e. …
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26 votes

What is the non-motivic motivation behind automorphic representations?

These are some comments that originally appeared on the OP's earlier question (linked above), gathered together here as an answer: The notion of automorphic representation (as an irreducible represen …
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14 votes
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Constructing coherent sheaves on Shimura varieties.

If the Shimura variety is attached to the Shimura data $h:\mathbb S \to G_{/\mathbb R}$, and if as usual $K$ denotes the centralizer in $G_{/\mathbb R}$ of $h$, then the automorphic vector bundles are …
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12 votes

p-adic L-functions

You should distinguish between the method (of which there is not one, but several) and the result (namely, the existence of $p$-adic $L$-functions). It is expected that $p$-adic $L$-function exist …
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11 votes

Unitary groups over number fields

Just to add to Jon Yard's answer: when one defines a unitary group as described in the OP, the group that one gets after extending scalars from $F$ to $F_v = \mathbb R$ for each archimedean place $v$ …
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