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Algebraic varieties, stacks, sheaves, schemes, moduli spaces, complex geometry, quantum cohomology.
0
votes
1
answer
387
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Rationality of Hilbert schemes?
Consider the Hilbert scheme of curves in $P^3$ with genus $g$ and degree $d$, $H_{g,d}$. Is this rational for some $g$ and $d$?
Edit: For which $(g,d)$ is this rational?
1
vote
1
answer
209
views
Let $X$ be a projective variety. Is the bounded derived category of perfect complexes admiss...
By an admissable subcategory $A$ in a triangulated category $B$, I mean a triangulated subcategory that has $A \oplus B \in A$, then $A$, $B \in A$, and so that there is either a right or left adjoint …
7
votes
0
answers
292
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How are moduli stacks used?
Can someone give me an indication or reference for a situation in which the geometry of some moduli stack is "used"? I know that intersection theory and cohomologies can be developed on algebraic stac …
5
votes
1
answer
350
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If $X$ is a degree 3 smooth integral surface in $P^N$, $N > 3$, is it still true that it con...
It is a well known fact that a smooth cubic surface in $P^3$ contains 27 lines. One proof proceeds by moving through the parameter space $U$ of smooth cubics until one reaches an cubic that can be und …
8
votes
1
answer
340
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Objects of a category of homological dimension 1 is a smooth stack?
I heard a reference to a statement like:
Suppose $A$ is an (Abelian?) category of homological dimension one, then the stack of objects of $A$ is smooth. (I am not really sure what the stack of object …
5
votes
0
answers
713
views
Ehresmann's without properness in the algebraic category?
Ehresmann's theorem for manifolds states: If $f : X \to Y$ is a proper submersion, then $X$ is a locally trivial fibration on $Y$.
Some sources I am reading (Lazarsfeld Positivity in Algebraic Geomet …
5
votes
1
answer
458
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Polynomial size embeddings of toric varieties from polytopes?
Background: Let $P$ be a integral polytope, and $X_P$ the toric variety associated to the normal fan.
$X_P$ is always projective, because the collection of characters corresponding to the points $\ma …
1
vote
Polynomial size embeddings of toric varieties from polytopes?
I think I found an a example of a family of toric varieties whose minimal embedding dimension is exponential in their dimension. The idea is to produce a singular point with a high dimensional tangent …
34
votes
2
answers
926
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If $A$ is the ring of continuous functions on a genus $g$ surface, can the genus of $X$ be s...
I was describing to a friend the result that a compact Hausdorff space is determined up to homeomorphism up to by its ring of continuous functions, and he asked how one could see the genus of a surfac …