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Algebraic varieties, stacks, sheaves, schemes, moduli spaces, complex geometry, quantum cohomology.
16
votes
Birationally transforming a quartic elliptic curve
The method explained in Husemöller's book on elliptic curves is as follows:
Take a general quartic $v^2=f_4(u)=a_ou^4+a_1u^3+a_2u^2+a_3u+a_4$, and let
$$u=\frac{ax+b}{cx+d}\qquad v=\frac{ad-bc}{(cx+d) …
2
votes
Equivalence of various definitions of arithmetic Chow groups
The general idea is that for an arithmetic variety $X$, different choices of the pair $(H^\bullet,\mathcal{C})$, where $H^\bullet$ is a cohomology theory and $\mathcal{C}$ is a complex, yield differen …
5
votes
Hodge standard conjecture in positive characteristic
Probably too late, but...
(1) Not quite. The Hodge index theorem only works for $\mathbb{C}$. To extend it to all characteristic $0$ ground fields, you need the Lefschetz principle and the comparison …
1
vote
Accepted
Algebraic proof of Ramanujam's vanishing theorem
Perhaps this helps: Kyungho Oh, Vanishing Theorems for Singular Varieties, (Proceedings of the American Mathematical Society).
1
vote
Kummer extension of Galois modules
I'm not sure if this is what you are looking for, but consider the Tate curve $E_q$ on your local field $k$. It sits on the exact sequence of $G_k$ modules.
$$0 \to \mu_n \to E_q[n] \to \mathbb{Z}/n\ …
3
votes
Accepted
Why is $\mathbb{Q}_p(p^{1/p^\infty})$ a complete topological field?
This was alredy answered in the comments, it is the $p$-adic completion of $\mathbb{Q}_p(p^{1/p^\infty})$ that is a perfectoid field.
But here is a reference for completeness
Matthias Wulkau, Revie …
11
votes
When did "Betti cohomology" come to be used the way it is today? (and how is it used)
Some of this stuff is explained in much detail in this paper:
Charles Weibel, History of Homological Algebra (1999)
In particular, after reviewing the work of Riemman and Betti, it says:
Insp …
14
votes
0
answers
1k
views
Status of the "anabelian dream" ($\mathrm{dim} \leq 1$)
The anabelian conjectures for small dimensions have been known for quite some time. In full generality the results are:
Dimension 0. Finitely generated fields are anabelian (Pop)
Dimension 1. Hyperb …
30
votes
2
answers
5k
views
Grothendieck's "La longue Marche à travers la théorie de Galois"
It seems that Grothendieck's familly has given permission for the distribution of his unpublished works, so I hope it is ok to ask this.
Is there any way to obtain a copy (online or not) of "La lo …
19
votes
Accepted
Grothendieck's "La longue Marche à travers la théorie de Galois"
All the manuscripts have been finally made avaible by Montpellier university.
You can find all of them here, avaible in pdf.
The items related to “La longue Marche" are:
La "Longue Marche" à traver …
30
votes
Progress on the standard conjectures on algebraic cycles
For future references. Feel free to edit to include new cases, or any improvements.
As for 2015, the standard conjectures on algebraic cycles is unconditionally (at lest) known for $X$:
Lefschetz st …
12
votes
$\zeta(n)$ as a mixed Tate motive
Partially inspired by an unpublished work of Wojtkoviak for $\zeta (3)$, all of this follows from this result by Deligne:
Theorem. $\pi_1(\mathbb{P}^1-\{0,1,\infty\})$ is a smooth mixed Tate motive o …
4
votes
Accepted
Motivation for Hirzebruch-Jung Modified Euclidean Algorithm
I think the motivation for the Hirzebruch-Jung algorithm is not the algorithm itself, but the fact the it yields directly a very interesting continued fraction expansion. It is those, now called Hirze …
9
votes
Which elliptic curves over totally real fields are modular these days?
Elliptic curves over real quadratic fields were proven to be modular very recently by Freitas, Le Hung and Siksek:
Nuno Freitas, Bao Le Hung, Samir Siksek, Elliptic Curves over Real Quadratic Fields …
9
votes
Crystalline realization of mixed Tate motives
Apparently this issue was worked out shortly after, during Go Yamashita's stay at the IHES in 2006, and after some discussion with Deligne.
For any Tate motive $M$ unramified at $v$, its crystalline …