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

21 votes
Accepted

why we need rigid geometry?

I am really not an expert in the field, so I apologize in advance for omissions or mistakes - I would indeed be glad to get corrections. But let me try, anyhow... You are asking for a motivation for r …
Filippo Alberto Edoardo's user avatar
8 votes
1 answer
751 views

Honda-Tate in families

Let $k$ be a finite field, say with $q=p^a$ elements. Honda-Tate theory states that there is a bijection between isogeny classes of simple abelian varieties over $k$ and $\mathrm{Gal}(\overline{\mathb …
Filippo Alberto Edoardo's user avatar
4 votes
Accepted

Base change in crystalline cohomology?

You finish your question by insisting that the isomorphism be such but "not in the sense of derived categories", which I do not understand completely, since both objects you have at hands naturally li …
Filippo Alberto Edoardo's user avatar
1 vote

Topology on $p$-adic period ring in an article by Fontaine

I think a good reference is Schneider's book Nonarchimedean Funtional Analysis, but my answer is simply an expanded version of GTA's comments. In Chapter IV, §14, A and B you find a description of tw …
Filippo Alberto Edoardo's user avatar
17 votes
2 answers
2k views

Geometric interpretation of Hida isomorphism

[EDIT]: After getting a very nice answer by Kevin Buzzard I realize that my question was a little bit too vague and I try to restate it more precisely. As the title says, I would like to understand a …
Filippo Alberto Edoardo's user avatar
6 votes
Accepted

The $\ell$- part of the class groups of the $p$-cyclotomic fields

As Keith Conrad observed in his comment, what you are asking about is Washington's theorem which is either in his book, referenced as Theorem 16.12, or in his original paper in Invent. Math. He proved …
Filippo Alberto Edoardo's user avatar
1 vote
Accepted

Is Gouvêa-Mazur's "Infinite Fern" a fractal?

I post this as an auto-answer mainly not to leave the question open. After googling a bit better, I discovered two recent works by M. Lapidus and L. Hung (both available on Lapidus' webpage ) “Non …
Filippo Alberto Edoardo's user avatar
4 votes

The use of embedding a curve into its Jacobian

This is not really about the embedding, rather about the identification of points on the Jacobian with degree-0-divisors. If you are given a cuspidal form $f\in S_2(\Gamma_0(N),\mathbb{Q})$, by defini …
Filippo Alberto Edoardo's user avatar
2 votes
Accepted

Fontaine-Fargues curve and period rings and untilt

As Daniel Litt says, the choice of $C$ is actually an untilt. The "classical" approach to period rings, which you might have in mind, was to start with a certain complete, algebraically closed field $ …
Filippo Alberto Edoardo's user avatar
23 votes
Accepted

Proof of Prop 1.1 in Wiles' "Modular elliptic curves and Fermat's last theorem"

Well, although there is a typo (Wiles forgot to close his parenthesis, and wrote $H^2(G,\mu_{p^r}\to H^2(G,\mu_{p^s})$ in his proof), his claim is correct. Let, as ibid. $F$ be the finite extension of …
Filippo Alberto Edoardo's user avatar
7 votes
1 answer
940 views

Is Gouvêa-Mazur's "Infinite Fern" a fractal?

[EDIT]: Following Qiaochu Yuan's comment, it is better to clarify that I do not know what the right definition of a fractal in the following question should be. But a nice answer might contain such a …
Filippo Alberto Edoardo's user avatar
12 votes
Accepted

Adjoining torsion points from abelian varieties

If $\lambda\in\overline{\mathbb{Q}}$, the elliptic curve $$ E_\lambda\colon y^2=x(x-1)(x-\lambda) $$ has $(\lambda,0)$ as $2$-torsion point and is defined over (a subfield of) $L=\mathbb{Q}(\lambda)$ …
Filippo Alberto Edoardo's user avatar
3 votes
Accepted

Does Ribet's construction of class fields give us eigenspaces of rank 1?

I don't think we know how to prove this directly. Indeed, recent works by Wake and Wake–Erickson show that this cyclicity is equivalent to a conjectured improvement of Mazur–Wiles' result to the effec …
Filippo Alberto Edoardo's user avatar