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Prime numbers, diophantine equations, diophantine approximations, analytic or algebraic number theory, arithmetic geometry, Galois theory, transcendental number theory, continued fractions

36 votes

What is the L-function version of quadratic reciprocity?

Say $K=\mathbf{Q}(\sqrt{p^{*}})$ is the unique quadratic field in which $p$ is the only ramified finite prime. That is, $p^*=(-1)^{(p-1)/2}p$. There are two $L$-functions one can concoct out of $K$, …
Jared Weinstein's user avatar
16 votes
1 answer
566 views

The space of cusp forms for $\mathrm{GL}_2$ over ${\mathbf{F}}_q(T)$

This question is about automorphic forms for the group $\mathrm{GL}_2$, over a rational function field. Let's say $\mathbf{F}_q$ is a finite field, and $X=\mathbf{P}^1_{\mathbf{F}_q}$ is the projecti …
Jared Weinstein's user avatar
15 votes

modular eigenforms with integral coefficients [Maeda's Conjecture]

The statement that the Hecke algebra acts irreducibly on $S_k(\Gamma(1))$ is known as Maeda's conjecture, and it is still open. So an affirmative answer to your question about eigenforms with integer …
Jared Weinstein's user avatar
3 votes

Locally profinite fields ?

I was going to leave this as a comment, but I have a firm conviction about this, so here's my answer. The fields in your (1) are called (a) locally compact non-archimedean fields, or (b) non-archimed …
Jared Weinstein's user avatar
4 votes
Accepted

What is the base change in number theory?

In number theory, base change can also refer to an operation on automorphic representations. If L/K is an extension of number fields, and pi is an automorphic representation of a reductive group G ov …
Jared Weinstein's user avatar
11 votes
0 answers
376 views

What are the endomorphisms of Drinfeld's "special formal O_D-modules"?

Let $F$ be a nonarchimedean local field, and let $D/F$ be the central division algebra of invariant $1/d$. Let $k$ be the algebraic closure of the residue field of $F$ and let $\pi$ be a uniformizer. …
Jared Weinstein's user avatar
12 votes
2 answers
744 views

An isogeny between Jacobians of hyperelliptic curves

Let $\mathbf{F}_q$ be a finite field of odd characteristic. Let $X_t$ be the hyperelliptic curve over $\mathbf{F}_{q^2}(t)$ with affine equation $$y^2 = \left((x^{(q+1)/2}-(x-1)^{(q+1)/2})^2 - t\righ …
Jared Weinstein's user avatar
3 votes

p-adic representations of a quaternion algebra over a local field

If $E$ is an algebraic closure of $F$, then $D\otimes_F E\simeq M_2(E)$. (In fact this is also true if $E$ is taken to be, say, the unramified quadratic extension field of $F$.) We get an algebraic …
Jared Weinstein's user avatar
11 votes
0 answers
379 views

Galois invariants in a ring of fractional power series over a finite field

Let $\mathbf{F}_q$ be a finite field, and let $A=\mathbf{F}_q [[ x^{1/q^\infty} ]]$ be the completion of $\mathbf{F}_q[x^{1/q^\infty}]$ with respect to the $x$-adic topology. Then the $q$th power Fro …
Jared Weinstein's user avatar
23 votes
Accepted

Deligne's letter to Piatetskii-Shapiro from 1973

I have typeset Deligne's letter, and placed the result here: http://www.math.ias.edu/~jaredw/DeligneLetterToPiatetskiShapiro.pdf I have made some minor edits so that the text reads more naturally to …
20 votes

What's the "best" proof of quadratic reciprocity?

The proof involving Gauss sums always seemed the best to me. I'm going to run my own undergrad number theory students through that proof, right after we develop some experience with roots of unity. …
Jared Weinstein's user avatar
8 votes
1 answer
723 views

What are the automorphisms of a perfectoid Tate algebra?

Let $K$ be a complete nonarchimedean field. The classical Tate algebra $K\langle T \rangle$ has lots of automorphisms, e.g., any substitution $T\mapsto a_1T+a_2T^2+\cdots$, where $a_1\in \mathcal{O}_ …
Jared Weinstein's user avatar
28 votes
1 answer
2k views

How does Tate verify his own conjecture for the Fermat hypersurface?

This question is about Tate's 1963 paper "Algebraic Cycles and Poles of Zeta Functions". Here he announces a conjecture (now known as "the Tate conjecture") which states that certain classes in the c …
Jared Weinstein's user avatar
11 votes
Accepted

Geometric construction of depth zero local Langlands correspondence

Yoshida considers the Lubin-Tate tower in his geometric realization of the depth zero supercuspidals for $GL(n)$. For unitary groups, I'm sure that the answer to your question will be found in a simi …
Jared Weinstein's user avatar
20 votes
Accepted

"Purely local" proof of local Langlands

The short answer to the question is that all currently known proofs of the local Langlands correspondence (and I'm just referring to GL(n) here) are "global" in the sense that they involve embedding t …
Jared Weinstein's user avatar