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Algebraic varieties, stacks, sheaves, schemes, moduli spaces, complex geometry, quantum cohomology.

7 votes
2 answers
268 views

Examples of schemes $S$ with $H^{3}(S,\mathbb G_{m})=0$

The examples I have are: $S$ is equal to the spectrum of a global field; or a proper non-empty open subscheme of the spectrum of the ring of integers $\mathcal O_{K}$ of a number field $K$ (proper mea …
Cristian D. Gonzalez-Aviles's user avatar
3 votes
1 answer
263 views

Norm 1 (or trace 0) commutative algebraic groups

Let $F$ be a field and let $G$ be a smooth, commutative and connected $F$-group scheme of finite type. Let $K/F$ be a finite Galois extension of fields. Then there exists a canonical norm (or trace, i …
Cristian D. Gonzalez-Aviles's user avatar
0 votes
2 answers
178 views

Products of varieties of index 1

Let $k$ be a field of characteristic 0 and let $X$ and $Y$ be smooth, projective and geometrically integral $k$-schemes of finite type. Assume that both $X$ and $Y$ have 0-cycles of degree 1. Does $X\ …
Cristian D. Gonzalez-Aviles's user avatar
6 votes
0 answers
199 views

Units in $B\otimes_{A}B$, where $B/A$ is a finite Galois extension of number rings

I need information or directions to the literature regarding the structure of the group of units of $B\otimes_{A}B$, where $B/A$ is a finite Galois extension of rings of integers, say associated to a …
Cristian D. Gonzalez-Aviles's user avatar
7 votes
1 answer
453 views

Galois invariant line bundles on a product of varieties

Let $k$ be a field with separable algebraic closure $k^{\rm s}$ and corresponding absolute Galois group $\varGamma={\rm Gal}(k^{\rm s}/\,k)$ and let $X$ and $Y$ be geometrically connected and geometri …
Cristian D. Gonzalez-Aviles's user avatar
0 votes
Accepted

Products of varieties of index 1

The referee for one of my papers gave the following argument: Let $k$ be any field and let $X$ and $Y$ be smooth, proper and geometrically integral k-schemes of finite type. Let $x$ be a $0$-cycle on …
Cristian D. Gonzalez-Aviles's user avatar
7 votes
1 answer
586 views

Picard groups of reductive group schemes

There exists information on the Picard (and Brauer) group of a reductive algebraic group over a number field k. For example, Sansuc shows (in his big Crelle paper of 1980) that if G is connected and …
Cristian D. Gonzalez-Aviles's user avatar
6 votes
2 answers
403 views

A connected reductive algebraic group over a separably closed field is a rational variety

I need either a proof or a reference in modern (scheme-theoretic) language. According to Sansuc, this result can be gleaned from Borel's book on linear algebraic groups, but the old-style algebraic ge …
Cristian D. Gonzalez-Aviles's user avatar
13 votes
1 answer
670 views

The Picard group of a semisimple algebraic group in positive characteristic

Let $k$ be a field of positive characteristic and let $G$ be a connected semisimple algebraic group over $k$ with fundamental group $\mu$. Note that $\mu$ can be non-smooth. It is stated in Sansuc's 1 …
Cristian D. Gonzalez-Aviles's user avatar
2 votes

Quasi-compact surjective morphism of smooth k-schemes is flat

First of all, the version that we would like people to read (and hopefully check for more mistakes, if any remain) is the Arxiv version of our paper. We worked on that for 4 years and with great care. …
Cristian D. Gonzalez-Aviles's user avatar
7 votes
0 answers
277 views

Quadratic twists of 1-motives

Quadratic twists of elliptic curves (or, more generally, abelian varieties) are familiar objects in arithmetic geometry. I would like to extend that definition to the category of 1-motives over global …
Cristian D. Gonzalez-Aviles's user avatar
11 votes
1 answer
847 views

Sheaf associated to presheaf Aut

Let $S$ be a scheme and let $C$ be the category of schemes flat and locally of finite presentation over $S$. Endow $C$ with the fppf topology (or perhaps any subcanonical topology). Let $\mathcal P$ b …
Cristian D. Gonzalez-Aviles's user avatar