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Diophantine equations, rational points, abelian varieties, Arakelov theory, Iwasawa theory.

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
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
2 votes

Kernel of restriction in étale cohomology of curves over number fields

Even for 0-dimensional varieties over number fields, the statement of Poitou–Tate duality is much more subtle than this: it's not enough just to compare the kernels of base-extension to $\overline{K}$ …
David Loeffler's user avatar
7 votes

How is Taylor-Wiles patching "horizontal Iwasawa theory"?

I think your question already contains its own answer. In classical, "vertical" Iwasawa theory one studies class groups, or other arithetic widgets like elliptic curve Selmer groups, in a limit over $ …
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
5 votes

p-adic L functions from Selmer groups - how canonical are they?

All of your questions are undermined by the same fundamental issue: you cannot talk about "the" p-adic $L$-function in this generality, because there is no sensible definition of what a $p$-adic $L$-f …
David Loeffler's user avatar
18 votes

Are some congruence subgroups better than others?

This question already has multiple nice answers, but I am going to add one more thing which isn't quite covered by the existing posts. One distinctive advantage of the $\Gamma_0(N)$ and $\Gamma_1(N)$ …
David Loeffler's user avatar
10 votes
Accepted

Definition of modular curve associated to $\Gamma(N)$

This is a subtle issue (which has come up before on this site several times, see e.g. is the modular curve X(N) defined over Q? for a related question). Your $S(N)$ is naturally a scheme over $\mathbb …
David Loeffler's user avatar
13 votes
Accepted

Definition of locally symmetric space of reductive groups

There is a very natural, intrinsic definition of a "symmetric space", as a manifold (Riemannian or Hermitian) with an extra symmetry of a certain prescribed type. It is then a theorem, not a definitio …
David Loeffler's user avatar
13 votes
Accepted

Do people prefer working on $\mathrm{GSp}$ and $\mathrm{GU}$ rather than $\mathrm{Sp}$ and $...

Symplectic case: Here are two reasons (not necessarily the only ones) why $\operatorname{GSp}_{2n}$ is more convenient to work with than $\operatorname{Sp}_{2n}$. Firstly: there is no Shimura datum w …
David Loeffler's user avatar
3 votes
Accepted

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

I remember discussing this with Emmanuel Kowalski not long ago. The short answer is that generalising the result to $J_1(N)$ is an open problem, and seems to be very difficult.
David Loeffler's user avatar
2 votes
Accepted

Why does $[I](P)=0$ ($P\in E$) imply $[\psi(I)](P)=0$ ? ($\psi$ is Hecke character of ellipt...

This is essentially the same as your other recent CM-theory question, in a mild disguise; for both questions the point is that $\psi(I)$ is a generator of $I$. This follows easily from the fact that $ …
David Loeffler's user avatar
12 votes

Simple motivation to study arithmetic geometry

Let $n$ be a prime number which has remainder 5 or 7 on division by 8. Then there exists a right-angled triangle with integer side lengths whose area is $n$ times a square. This is a theorem of Paul M …
David Loeffler's user avatar

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