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For questions about the derived categories of various abelian categories and questions regarding the derived category construction itself.

2 votes
0 answers
138 views

Is there any numerical obstruction for all perfect complexes on a scheme being strictly perf...

Let $X$ be a scheme and $E^{\cdot}$ be a cochain complex of sheaves of $\mathcal{O}_X$-modules. We call $E^{\cdot}$ a strictly perfect complex if $E^{\cdot}$ is a bounded (in both direction) complex …
Zhaoting Wei's user avatar
  • 9,019
3 votes
1 answer
205 views

Is the image of a idempotent morphism in $\mathcal{K}(\mathcal{A})$ defined in the naive way?

Let $\mathcal{A}$ be an abelian category and $\mathcal{K}(\mathcal{A})$ be the homotopy category of chain complexes in $\mathcal{A}$. It is well-known that $\mathcal{K}(\mathcal{A})$ is idempotent com …
Zhaoting Wei's user avatar
  • 9,019
0 votes
0 answers
178 views

Is the inverse of the criterion of fully-faithfulness of derived tensor product also true?

Let $A$ and $B$ be differential graded algebras over a field $k$ and $D(A)$ and $D(B)$ be the derived categories of differential graded modules. Let $N$ be an $A$-$B$ bimodule. Then $(-)\otimes^{\mat …
Zhaoting Wei's user avatar
  • 9,019
0 votes
0 answers
114 views

Is the pull back of a compact generator under field extension again a compact generator?

Let $\mathcal{T}$ be a triangulated category which has arbitraty direct sums. An object $E\in \mathcal{T}$ is called compact if the functor Hom$(E,-)$ commutes with arbitrary direct sums. A compact ob …
Zhaoting Wei's user avatar
  • 9,019
2 votes
0 answers
232 views

What are the point-like objects in $D^b(X)$ when $X$ is an abelian variety?

Let $X$ be a projective variety over an algebraically closed field $k$ and $D^b(X)$ be the derived category of bounded complexes of coherent sheaves on $X$. Let $S$ be the Serre functor on $D^b(X)$. A …
Zhaoting Wei's user avatar
  • 9,019
2 votes
0 answers
100 views

Could we construct an inverse transform for the equivalence $D^b(X)\to D^b(M)$ between a K3 ...

Let $X$ be a K3 surface and fix an ample line bundle on $X$. Let $v\in \widetilde{H}(X,\mathbb{Z})$ be a Mukai vector and $M(v)$ be the moduli space of semi-stable coherent sheaves on $X$ with Mukai v …
Zhaoting Wei's user avatar
  • 9,019
1 vote
0 answers
125 views

Does the Mukai's lemma hold for non-algebraic $K3$ surfaces?

In Huybrechts' book Fourier-Mukai Transforms in Algebraic Geometry I found the following result due to Mukai (Page 232, Lemma 10.6) Let $X$ and $Y$ be two $K3$ surfaces. Then the Mukai vector of any o …
Zhaoting Wei's user avatar
  • 9,019
4 votes
0 answers
344 views

Does derived equivalence imply dg Morita equivalence between DG algebras over field with cha...

Let $A$, $B$ be two DG algebras and $D(A)$, $D(B)$ be derived categories of DG-modules of $A$, $B$, respectively. We call $A$ and $B$ are dg Morita equivalent if there is an $A$-$B$ bimodule $T$ with …
Zhaoting Wei's user avatar
  • 9,019
6 votes
2 answers
1k views

Is there a compact generated triangulated category which does not have a compact generator?

Let $\mathcal{T}$ be a triangulated category which has arbitraty direct sums. An object $E\in \mathcal{T}$ is called compact if the functor Hom$(E,-)$ commutes with arbitrary direct sums. A triangula …
Zhaoting Wei's user avatar
  • 9,019
8 votes
1 answer
1k views

Can we define the tensor product in the derived category $D^b_{\text{coh}}(X)$ just from $D^...

This question arise from the comparision of the reconstruction theorems of Bondal-Orlov and Balmer and is inspired by Shizhuo Zhang's mathoverflow question: How to unify various reconstruction theorem …
Zhaoting Wei's user avatar
  • 9,019
12 votes
1 answer
638 views

An example of an object in $D^b_{\text{coh}}(\mathbb{P}^2)$ which is not formal

We know that for a curve $X$, any object $\mathcal{E}^{\bullet}$ in the derived category $D^b_{\text{coh}}(X)$ is formal, i.e. $\mathcal{E}^{\bullet}$ is quasi-isomporphic to the direct sum of its co …
Zhaoting Wei's user avatar
  • 9,019
3 votes
0 answers
422 views

Do all full exceptional sequences of a triangulated category have the same length?

Let $\mathcal{D}$ be a $k$-linear triangulated category and $\langle E_n,E_{n-1},\ldots, E_0\rangle$ be a sequence of objects of $\mathcal{D}$. We call $\langle E_n,E_{n-1},\ldots, E_0\rangle$ an $\te …
Zhaoting Wei's user avatar
  • 9,019
1 vote
0 answers
143 views

Is there any explicit result on the triangulated category of singularities of a curve?

This question is related to this MO question. Let $X$ be a projective curve over a field $\mathbb{C}$. We have the bounded derived category of coherent sheaves $D^b_{coh}(X)$ and the derived category …
Zhaoting Wei's user avatar
  • 9,019
3 votes
1 answer
499 views

The Hochschild cohomology of a variety "with coefficient" in a vector bundle

This question is related to one of my previous question Do we have the following isomorphism for $\mathcal{Ext}$? Let $X$ be a smooth variety (over $\mathbb{C}$) and $\Delta: X \rightarrow X \times X …
Zhaoting Wei's user avatar
  • 9,019
1 vote
0 answers
56 views

Could we extend isomorphisms between cohomologies of h-injective complexes to h-injective co...

Let $R$ be an associative ring with unit and $I$ be a complex of $R$-modules. We call $I$ is h-injective if for any acyclic complex $T$ of $R$-modules, the mapping complex $\text{Hom}_R(T,I)$ is acycl …
Zhaoting Wei's user avatar
  • 9,019

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