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

1 vote

Changing the weight space for an eigenvariety

I think this question is based on a misconception. “Being an eigenvariety” isn’t a rigorously defined property of a space (or map of spaces) which you could prove to hold or to not hold. It’s more lik …
David Loeffler's user avatar
5 votes
2 answers
126 views

Residue of Dirichlet series at $s = 1$

Let $(a_n)_{n \ge 1}$ be a sequence of complex numbers, and suppose that the sequence has a well-defined "average", in the sense that $$ \lim_{N \to \infty} \frac{1}{N}\sum_{i = 1}^N a_i = R$$ for som …
4 votes

Finiteness and bounds for elliptic curves realizing a given galois representation

The set $\mathcal{L}_{\rho}$ is either empty, or a singleton finite. This follows from Faltings' isogeny theorem, which states that for any two elliptic curves (or, more generally, abelian varieties) …
David Loeffler's user avatar
26 votes
Accepted

Applications of Iwasawa Theory

Aha, an excuse to quote chunks of my most recent grant proposal :-) Iwasawa theory is heavily used in work on the BSD conjecture. For instance, the first positive result to be proved in the direction …
Viktor Vaughn's user avatar
5 votes

Reference Request: Beilinson-Bloch conjecture in terms of Beilinson regulator isomorphism

Some conjectures – like this one and also the BSD conjecture – are hard to find in precise form in a single place, because the community's understanding of statement of the conjecture changed over tim …
David Loeffler's user avatar
6 votes
Accepted

Evidence for the equivariant BSD conjecture with higher multiplicity

You might want to study the work of Darmon--Lauder--Rotger, notably this paper: https://web.mat.upc.edu/victor.rotger/docs/DLR1.pdf They study cases of the equivariant BSD conjecture where $\rho$ is a …
David Loeffler's user avatar
5 votes
Accepted

Bounding $H^4_{\text{ėt}}$ of a surface

Are you absolutely sure you want to compute $p$-adic etale cohomology for a smooth proper $\mathbb{Z}[1/S]$-scheme with $p \notin S$, so $p$ is not invertible on $X$? This will be painful, and I stron …
David Loeffler's user avatar
5 votes

Reference Request: Test vectors for local Rankin-Selberg L-factors in ramified cases

Are you asking for a proof of existence, or an explicit construction? These are very different things! It is immediate from the definition that there exists a finite family $(W_i, W_i')_{i \in I}$ wit …
David Loeffler's user avatar
4 votes
1 answer
180 views

New vectors for representations of GSp4 with nontrivial central character

Roberts and Schmidt have developed a theory of new vectors for generic irreducible smooth representations of $\operatorname{PGSp}_4(F)$ for $F$ a nonarchimedean local field, using the "paramodular sub …
3 votes
Accepted

New vectors for representations of GSp4 with nontrivial central character

I'm adding an answer to this very old question of mine, since someone just contacted me about it. The problem is rather comprehensively solved in this 2019 preprint of Taeko Okazaki: Takeo Okazaki, L …
David Loeffler's user avatar
10 votes
Accepted

Understanding absolute Galois group from its representations

The slogan "number theorists aim to understand $\operatorname{Gal}(\overline{\mathbb{Q}} / \mathbb{Q})$" is one that gets used a lot, but it's perhaps a tiny little bit misleading. Understanding the s …
David Loeffler's user avatar
2 votes
Accepted

Variants of the classical Satake classfication

(1) Borel's article in the Corvallis proceedings does this slightly differently: he chooses a specific Frobenius element $\sigma$, and then looks at the subset $\widehat{G} \times \{\sigma\}$ of ${}^L …
David Loeffler's user avatar
6 votes
Accepted

Cohomology of Shimura varieties before and after completion at some prime

Yes, this is true. It works with arbitrary algebraic varieties, no need to be specific to Shimura varieties. Let $X \to^{\pi} Spec(K)$ be an algebraic variety, $\mathcal{F}$ an etale sheaf on $X$, and …
David Loeffler's user avatar
7 votes
1 answer
199 views

Lifting SL2(k) to a subgroup of Witt vectors

$\DeclareMathOperator\SL{SL}\DeclareMathOperator\GL{GL}\DeclareMathOperator\W{W}$Let $k$ be a finite field, and let $\W_n(k)$ be the degree $n$ Witt vectors over $k$ (so $\W_1(k) = k$). Does there ex …
5 votes
Accepted

Lifting SL2(k) to a subgroup of Witt vectors

I found the answer myself with the help of a very useful hint from user "nobody" in the comments, so I'm going to post a community-wiki answer in case anyone else finds it useful. My question is answe …
David Loeffler's user avatar

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