The coherent-sheaves tag has no wiki summary.
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1answer
177 views
Hilbert polynomial for any invertible sheaf
Let $X$ be a projective scheme over algebraically closed field $k$, $L$ is invertible sheaf on $X$ and $\mathcal F \in \operatorname{Coh}(X)$ , we define Hilbert polynomial $P_{\mathcal ...
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0answers
93 views
Help understanding the proof of a theorem about Cohomology of vector Bundles
I am trying to understand a paper called Betti tables of graded modules and cohomology of vector bundles, but i am stuck in Proposition 6.8 which states:
Let $\mathcal{E}$ be a vector bundle on ...
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0answers
52 views
Obstruction to the existence of global resolution of coherent sheaf
It is well known that any coherent sheaf on a complex manifold (or more generally a complex space) admits locally a resolution with locally free sheaves. It is also well known that for non-algebraic ...
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100 views
G-equivariant coherent sheaves on Bott-Samelson Resolutions
Let $G$ be a Lie group, $B$ be a Borel subgroup. $G/B$ is the corresponding flag variety.
Let $w$ be an element of the Weyl group $W$ with a reduced expression
$w = s_1 \cdots s_n$. Let $X_w$ be ...
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2answers
415 views
modular forms, invertible sheaves, and quotients
I'm very confused about some contradicatory statements, and I hope someone can help me clarify this.
Let $\Gamma$ be a congruence subgroup. It is well known that modular forms of weight $k$ for ...
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184 views
Can Kuranishi families glue together to give a moduli space?
In his article "Moduli spaces of vector bundles on K3 surfaces and symplectic manifolds", Mukai constructs moduli of simple sheaves on a K3 surface through a theorem that asserts the existence of a ...
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1answer
119 views
A canonical algebra of type $(2,2,r)$ is derived equivalent to a path algebra of type $\tilde{D}_{r+2}$ (references)
According to several articles I could find, a canonical algebra of type $(2,2,r)$ is derived equivalent to a path algebra of type $\tilde{D}_{r+2}$, where $r \geq 2$.
I don't know how to obtain this ...
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0answers
91 views
K-theory of ringed spaces (including henselian and formal schemes); excision and Mayer-Vietoris
Given a ringed topological space $S$ one can easily define its K and K'-theory as the K-theories of the categories of locally free sheaves and of the category of coherent sheaves on it, respectively. ...
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1answer
116 views
Iterated extensions of quotients of vector bundles
Let $X$ be a noetherian scheme. Consider the smallest class $\mathcal{S}$ of coherent sheaves on $X$ which has the following closure properties:
Every locally free sheaf is in $\mathcal{S}$.
If $A,B ...
2
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2answers
213 views
Some questions on vanishing of Ext sheaves
Let $X$ be a complex manifold of dimension $3$ and $\mathcal{E}$ be a coherent sheaf such that $\dim supp(\mathcal{E})=1$. In this situation, I would like to know why we have the Ext sheaf ...
2
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0answers
218 views
Cech cohomology.
Let us consider the scheme $X$ and the coherent sheaf $\cal F$ on it. We consider finitely many affine open covers $U_{\lambda}$ with $\lambda \in \Lambda$. When I calculate Cech cohomology with ...
2
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1answer
201 views
Non-separatedness of moduli space of sheaves
The moduli space of sheaves over a smooth variety is in general not separated. That is, there exists a flat family of coherent sheaves over a punctured disk which extends to a flat family of coherent ...
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1answer
233 views
Global to local for Ext groups and Sheaves
Let $X$ be a projective variety. The sheaf $\mathcal{E}xt^{1}(\Omega_{X},\mathcal{O}_{X})$ is supported on $Sing(X)$.
Now, there should be a theorem (perhaps by Schlessinger) that says that if $X$ ...
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1answer
179 views
Extend morphism between coherent sheaves in $\mathbb{P}^n$
Let $\mathcal{F}_1, \mathcal{F}_2$ be coherent sheaves over $\mathbb{P}^n_{\mathbb{C}}$ for $n \ge 3$. Now, $\Gamma_*(\mathcal{O}_{\mathbb{P}^n})=\mathbb{C}[X_0,...X_n]$. Denote by $U_0$ the affine ...
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1answer
206 views
Grothendieck duality for stacks
Let $\mathcal{X}$ be a smooth, proper and separated Deligne-Mumford stack and let $\pi:\mathcal{X}\rightarrow X$ be its coarse moduli space. Does Grothendieck duality hold for the morphism $\pi$ ?
In ...
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49 views
Convolution of DQ-Modules
On page 92 of Deformation Quantization Modules Kashiwara and Schapira define two different convolution products for DQ-modules that differ by whether one uses $Rp_{13*}$ or $Rp_{13!}$ to push ...
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182 views
what is the zero locus of a morphism of the derived category?
For a morphism of quasi-coherent sheaves $v\colon E \to F$, on a scheme $X$, one can ask about the locus where $v =0$.
When $F$ is a vector bundle, it's easy to see that this locus is closed.*
Is ...
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1answer
163 views
Do there exist equivariant sheafs that are not equivariant vector bundles?
For $F \subset G$ two algebraic groups, consider a homogeneous space $H$ of the form $G/F$. Now every vector bundle over $H$ is a coherent sheaf, but the converse is not true. What happens in the ...
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863 views
is the category of coherent sheaves some kind of abelian envelope of the category of vector bundles?
This might be obvious to experts, but I'm not sure where to look for the answer. On a reasonably nice, at least noetherian, scheme (or variety, algebraic space, stack), can the category of coherent ...
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0answers
199 views
Admissible subcategories of $D^b(\mathbb{P}^n)$
Recall that a triangulated subcategory $\mathcal{A}$ of a triangulated category $\mathcal{B}$ is called admissible if the inclusion functor has both left and right adjoints.
Is it true that all ...
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0answers
234 views
Global sections of a coherent sheaf in terms of a presentation
Let $A$ be a graded ring satisfying the usual finiteness conditions of EGA II (for example $A_0$ is noetherian, $A_1$ is finite over $A_0$ and $A$ is generated by finitely many elements of $A_1$ as an ...
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0answers
204 views
Base change for complex of coherent sheaves
I wonder if the base change for a flat complex of coherent sheaves works. Namely, let $f : X \rightarrow Y$ be a proper morphism of varieties over $k$. Let $\mathcal{F}^{\bullet}$ be a bounded complex ...
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98 views
Realization of a formal duality isomorphism via integration
This is a more precise version of my previous question. Let $X$ be a smooth variety of dimension $n$ over $\mathbb{C}$ and $Z$ a proper sub-scheme. We denote by $\tilde{X}$ the formal completion of ...
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152 views
The support of a finite type module on an algebraic space
I'd like to ask this question to make sure I understand a very basic thing about supports. Let $X$ be an algebraic space and F a quasi-coherent sheaf on it of finite type.
In here the schematic ...
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1answer
197 views
what are mutations of sheaves all about?
Suppose I have a smooth projective variety $X$ and a semi-orthogonal decomposition of its bounded derived category of coherent sheaves $D^b(X)$. Then I can apply right or left mutations to the full ...
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1answer
593 views
Coherent Sheaves and Holomorphic Vector Bundles
For a complex manifold $M$, I'm trying to understand (from a differential geometry point of view) what its category of coherent sheaves is. If I understand correctly, then the sheaf of holomorphic ...
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1answer
199 views
The locus where a sheaf is supported in a certain dimension
I am trying to understand a particular case of this question.
Let $T$ be an affine scheme of finite type over the ground field C. Let $X \to T$ be a morphism. I'll assume this to be the base change ...
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2answers
526 views
English reference for the Grauert–Riemenschneider vanishing theorem
What is the best reference in English for the following theorem of Grauert–Riemenschneider:
Theorem:
Let $\phi:X \to Y$ be a proper bi-rational morphism of algebraic varieties over characteristic ...
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0answers
103 views
coherent sheaves
suppose $X$ is a smooth variety, with a finite open covering $U_i, i=1,....,k$.
$F$ and $G$ are coherent sheaves on $X$, and $G$ is locally free.
Suppose on each $U_i$, there is a sheaf morphism ...
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3answers
247 views
restriction of sheaf
suppose X is a smooth variety and F is a locally free sheaf on X. Let U be an open subset of X and i denote the inclusion map.
Is i_*i^*F equal to F ?
thanks.
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1answer
128 views
Surjective and injective criteria via Hilbert polynomials
Let $X$ be a projective complex manifold. Is it true that any coherent sheaf $\mathcal{E}$ on $X$ whose Hilbert polynomial is a constant has a surjective morphsim $\mathcal{O}_X\rightarrow ...
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Def-Obs theory of sheaves with fixed determinant on CY3.
Let $\mathcal{E}$ be a stable sheaf on a smooth complex projective threefold $X$ and $Ext^k_0(\mathcal{E},\mathcal{E})$ be the traceless Ext groups, defined by the kernel of the trace map
$$
...
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1answer
130 views
Some bounded theorem of algebraic stack of coherent sheaves
Let $X$ be a connected projective scheme. Let $U$ be a finite type open substack of the algebraic stack of coherent sheaves on $X$ with a fixed Hilbert polynomial. Can one take $p>0$ such that ...
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1answer
586 views
got any tricks to build up t-structures on derived categories?
Are there any good tricks to construct a heart of a t-structure? (I'm thinking on the derived category of coherent sheaves of some variety)
I'll start with the only one I know. If $(T,F)$ is a ...
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2answers
215 views
Total exterior Product
In his paper Gaussian maps and plethysm, Manivel uses the term "total exterior product" of line bundles, appearing for the first time on page 3. Given two (projective) varieties $V_1$ and $V_2$ and ...
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2answers
653 views
Can one prove vanishing of higher direct images fiber-wise?
Let $\pi:X\to Y$ be a proper map of algebraic varieties (over $\mathbb C$) which is a bi-rational equivalence.
are the following statements equivalent?
The derived direct image of $O_X$ is $O_Y$.
...
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1answer
499 views
Is the bounded derived category of coherent sheaves of a variety a small category?
The question is in the title.
I am trying to apply the Mitchell (Freyd-Mitchell?) embedding theorem, which states that for every small abelian category $A$, there exists a ring $R$ such that A ...
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1answer
534 views
Proper morphism sending coherent to coherent
Hello,
Is there a proof that the push forward by a proper morphism of Noetherian schemes sends coherent sheaves to coherent ones, without passing in the argument through projective morphisms?
Thank ...
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0answers
166 views
Do infinitesimal neighbourhoods help to compute the inverse images of coherent sheaves?
Let $i:Z\to X$ be a closed embedding of (projective) varieties; $S$ is a coherent sheaf on $X$. How could one compute $H^*(Z,i^\ast S)$ (I don't know whether I should write $H^\ast (Z,i^{-1}S)$ ...
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1answer
277 views
can one define the pullback between stacks of coherent sheaves for non-flat morphisms?
Consider a morphism $f: Y \to X$ between two varieties and consider the stacks parametrizing coherent sheaves on them $\mathcal{M}_X, \mathcal{M}_Y$.
Does one have for free an induced pullback ...
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2answers
517 views
Local freeness of direct images
This question arose from an unsuccessful attempt to settle another question of mine: Vector fields on complete intersections
Let $X\to Y$ be a smooth projective morphism of noetherian schemes and let ...
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3answers
1k views
Derived categories of (coherent) sheaves of modules: exceptional images, gluing, and proper descent?
I am interested in the properties of (the derived categories) of various categories of (coherent) sheaves of modules (over varieties). I would like to understand in what extent these properties are ...
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1answer
306 views
Do some of the local cohomology groups of the structure sheaf on the singular locus vanish?
Ok, so this is where I reveal my ignorance as an algebraic geometer: I had previously asked about pushforward of line bundles from the smooth locus of a variety to the whole thing. I think I ...
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3answers
908 views
Is the pushforward of a line bundle on the smooth locus of a terminal singularity again a line bundle?
In algebraic geometry, it is a sad fact of life that pushforward doesn't preserve being a coherent sheaf; for example, the pushforward by the complement of a divisor of the structure sheaf (or more ...
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2answers
616 views
coherent sheaves on affine formal schemes
Let $\hat{X} = \text{Spf} \hat{A}$ be obtained as the formal completion of an affine scheme $X = \text{Spec} A$ where $A$ is an adic noetherian ring. Given a coherent sheaf $\mathfrak{F}$ on ...
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1answer
479 views
Coherent sheaves on projective space over a general ring
Let $K$ be a field and $n \geq 0$. Serre proved that $\text{Qcoh}_f(\mathbb{P}^n_K)$ is equivalent to the localization of $\text{grMod}_f(K[x_0,...,x_n])$, in which the inclusions $M_{\geq a} \to M$ ...
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1answer
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question about torsion sheaf
Hi, i'm stuck on the following, please can someone help?
Let $E$ be a complex holomorphic vector bundle of rank r over a compact kahler
manifold $M$, let me indicate $\mathcal{E}$ the associated ...
3
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1answer
232 views
Semicontinuity and cohomological flatness for algebraic spaces
Let $f \colon X \to S$ be a proper morphism form a seperated algebraic space $X$ to an affine noetherian scheme $S$.
Given a coherent sheaf $F$ on $X$, we know from Knutson's book, that the ...
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3answers
1k views
Is it true that if the pushforward of a coherent sheaf is locally free, then the original sheaf is locally free?
I think the title says it all. If I have a finite map $p:X\to Y$ between schemes, and $F$ is a coherent sheaf on $X$ such that $p_*F$ is locally free, can I conclude that $F$ is locally free?
...
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2answers
568 views
Deformations of sheaves via automorphisms. How to express $Ext^1$?
Let $X$ be a complex manifold (for example $\mathbb CP^n$), let $v$ be a holomorphic vector field on $X$, and let $F$ be a coherent sheaf (for example a vector bundle or a structure sheaf of a point). ...
