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

0 votes

Projective submanifolds of $\mathbb CP^n$ whose normals bundles are sums of linear.

For sure if the variety is a complete intersection then the normal bundle splits. I am afraid that the other way round is not true. IMO it should imply just being locally complete intersection, and a …
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1 vote

hyperelliptic stable genus four curve

All smooth genus four curves have two $g^1_3$. Since the unviersal picard fibration over the moduli space of stable genus four curves is proper, yes you can assume that the generic fiber is hyperellip …
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2 votes

blow-ups of secant varieties

You can probaly describe your space as some kind of fibration in $\mathcal{M}_{0,m}$ over the dual linear system $\mathbb{P}^{n*}$, via Kapranov's blow-up construction of $\overline{\mathcal{M}_{0,m}} …
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6 votes

arithmetic genus of nonsingular curve of degree d in PP^3

$\frac{1}{2}(d-1)(d-2)$ is the genus of a smooth plane curve of degree $d$. If you project from $P^3$ to $P^2$ off a point not contained in $C$ you can always get a plane curve of the same degree with …
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1 vote
0 answers
227 views

generalized Noether-Lefschetz Theorem

I have always had problems in understanding what people mean when they say "the generalized Theorem of ...". For instance, I seem to understand that there are a few different generazlized Noether-Lefs …
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1 vote

The degree of the hypersurface of pfaffian cubic fourfolds

Just a remark: the Pfaffian locus is not quite the $\mathcal{C}_{14}$ divisor, but rather a constructible dense subset of $\mathcal{C}_{14}$, see https://link.springer.com/article/10.1007/s00208-018 …
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0 votes
1 answer
148 views

pullback of certain forms

Let $p : W \rightarrow S$ be a smooth morphism of algebraic varieties over $\mathbb{C}$. Is it always true that: $$p^*H^{p,n-p}(S)=p^*H^n(S,\mathbb{C})\cap H^{p,n-p}(W),$$ whenever $n\geq p$? If not …
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4 votes
1 answer
198 views

Reference for definition of residue of a differential form, in all characteristics

What is the standard reference for a definition , valid in all characteristics, of the residue in a point of a rational differential form on a curve?
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0 votes
1 answer
258 views

Koszul complex of a variety inside a product

Suppose $X$ is a smooth projective complete intersection contained in the product $\mathbb{P}^n \times \mathbb{P}^m$, and call $X_n$ and $X_m$ the images of $X$ inside $\mathbb{P}^n$ and $\mathbb{P}^m …
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2 votes
2 answers
159 views

normality of moduli of prym curves

Is the moduli space of Prym curves (curves $C$ with square root of $\mathcal{O}_C$, compactified via admissible covers - by Beauville) of a given genus $g$ normal? Why?
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-1 votes

Is very ampleness of a divisor on a curve determined entirely by degree and genus?

I am maybe misunderstanding, but I think that ypur example is fulfilled by a couple of curves of gwnus bigger than 3, one hyperelliptic and the other not. If you consider the canonical divisor, it is …
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4 votes
2 answers
433 views

Hasse principle for high dimensional varieties

What is the state-of-the-art of the proof/counterexamples of the Hasse principle for high-dimensional hypersurfaces (say 3-folds or more)?
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0 votes

When does a G-invariant one to one map between two closed algebraic G-set descend to a one t...

as long as $f$ passes to the quotient (i.e. sends orbits on orbits) it has the required property. Moreover, as Misha remarked, the semistable locus of the first quotient should be sent to the semistab …
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0 votes

smooth modular compactification of moduli of curves

$\mathbb{P}^3$ compactifies the moduli space of genus 2 curves with level 3 structure and the choice of an odd theta characteristic.
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-1 votes

Albanese dual to the Picard scheme

I like very much Mumford's "abelian varieties", which has the advantage to work over any characteristic. enjoy!
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