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for questions on one dimensional algebraic varieties over any field, including questions of moduli, and questions about specific curves.

4 votes
1 answer
541 views

Curves and semi-abelian varieties

Fix $k$ a number field, and let $C$ be a smooth geometrically integral affine curve over $k$. We can "associate" to $C$ a semi-abelian variety in the following way: One knows that $C$ is a finite numb …
oleout's user avatar
  • 895
3 votes
1 answer
254 views

If a genus 2 curve has no $k$-rational points, can it have a $k$-rational divisor class of d...

Let $C$ be a smooth projective geometrically connected curve of genus 2 defined over a number field $k$. Here are some definitions: The index $I$ of a curve $C$ is the greatest common divisor of all e …
oleout's user avatar
  • 895
3 votes
0 answers
167 views

Injectivity of the Abel map away from singularity

It is known that a smooth projective curve $C$ of genus $\geq 1$ over $\mathbb{C}$ embeds into its Jacobian $J(C)$, via the isomorphism $J(C) \cong \mathrm{Pic}^0(C)$. Question 1. Is this embedding st …
oleout's user avatar
  • 895
2 votes
1 answer
312 views

Computing $H^1$ with coefficients in a torsion-free abelian group

Let $k$ be a number field and denote by $H^i(k,-)$ the Galois cohomology functor $H^i(\mathrm{Gal}(\bar{k}/k),-)$. Let $X$ be a smooth geometrically integral curve over $k$. One can easily show that t …
oleout's user avatar
  • 895
1 vote
1 answer
340 views

The smooth completion of a curve

Let $C$ be a smooth geometrically integral affine curve. This question concerns the smooth completion $C_1$ of $C$, both defined over a number field $k$. We know that given any smooth projective geome …
oleout's user avatar
  • 895
1 vote
1 answer
176 views

The groups $H^i(k,\mathbb{Z})$ for $i=1,2$

This question is related to my post Interpretation of some maps involving cohomology groups. $C$ is a smooth geometrically integral affine curve over a number field $k$, and $C_1$ is its smooth comple …
oleout's user avatar
  • 895
1 vote
0 answers
191 views

Brauer-Manin obstruction and affine curves

I'm looking for references that can justify to what extent is the following statement true: Statement. Let $X$ be a smooth geometrically integral curve over a number field $k$. Then the Brauer-Manin o …
oleout's user avatar
  • 895
1 vote
1 answer
319 views

Counterexample to purity of Brauer group for curves

The purity of Brauer group states that for a smooth (quasi-)projective variety $X$ over a field $k$, removing a closed subscheme $Z \subset X$ of codimension at least $2$ ensures that the restriction …
oleout's user avatar
  • 895
1 vote
0 answers
110 views

Is it possible to define the generalized Jacobian of a curve when the modulus $\mathfrak{m}$...

The book Algebraic groups and class fields by Serre explains a lot about the construction of the generalized Jacobian $J_\mathfrak{m}$ of a smooth projective curve $X$ with respect to the modulus $\ma …
oleout's user avatar
  • 895
1 vote
0 answers
158 views

The $H^1$ of a smooth curve and its (generalized) Jacobian variety

Let $C$ be a smooth projective curve of genus $\geq 1$ over a number field $k$ with a $k$-rational divisor of degree $1$ inducing the embedding $C \hookrightarrow J$, where $J$ is the Jacobian variety …
oleout's user avatar
  • 895
0 votes
0 answers
202 views

Cohomology map induced by inclusion of curves

Let $C$ be a smooth affine geometrically integral curve of genus $\geq 1$ over an algebraically closed field $k$, and let $\iota: C \rightarrow C'$ denote the inclusion into its smooth compactificatio …
oleout's user avatar
  • 895
0 votes
0 answers
111 views

For curves $C$ of genus $1$, the period (or index?) of $C$ is greater than $1$ iff $C(k)$ is...

As the title suggests, does anyone have a reference for the proof of this fact? Actually, I can't remember where I've seen it before, or if I even remembered the statement correctly. Here are some con …
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  • 895
0 votes
0 answers
61 views

A non-ordinary singularity "splitting" into another non-ordinary singularity on a curve

The classical book of Walker on algebraic curves described a method of computing the genus of curves with non-ordinary singularities by transforming such a curve into a birational one with only ordina …
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  • 895