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Algebraic varieties, stacks, sheaves, schemes, moduli spaces, complex geometry, quantum cohomology.
37
votes
3
answers
6k
views
Conjectures in Grothendieck's "Pursuing stacks"
I read on the nLab that in "Pursuing stacks" Grothendieck made several interesting conjectures, some of which have been proved since then. For example, as David Roberts wrote in answer to this questi …
41
votes
A bestiary of topologies on Sch
I have just discovered a chart comparing topologies on Sch/S, made by Pieter Belmans. It includes all the topologies discussed above, and some more I haven't even heard of. It's even interactive and …
17
votes
Why is the motivic category defined over the site of smooth schemes only?
It makes sense to consider larger versions of the (unstable and stable) motivic homotopy categories built out of the site $Sch_S$ of all schemes over $S$ (say of finite type to avoid dealing with size …
12
votes
Accepted
A question on Voevodsky´s categories
One could say that the story begins with Beilinson's conjectures on the existence of a theory of motivic cohomology. In accordance with the insights of the Grothendieck school that cohomology theorie …
24
votes
Why do we need model categories?
This answer is an elaboration on Dylan's comments.
1) Let us define a homotopy theory to be a pair $(C, W)$, where $C$ is a category and $W$ is some class of morphisms called weak equivalences.
(Let' …
83
votes
Accepted
Derived algebraic geometry: how to reach research level math?
I propose the following plan, assuming a basic background in scheme theory and algebraic topology. I assume that you are interested in derived algebraic geometry from the point of view of application …
3
votes
Accepted
When is a sheaf coherent if its image under a Fourier-Mukai transform is coherent?
Your proof works in the derived case as well.
That is, assume smoothness so that $D^bCoh$ is identified with the full subcategory of compact objects (in general the argument will apply to the subcate …
8
votes
Accepted
Relations between Motivic Galois groups and Motivic t-structure?
The argument sketched in Example 3.20 of [J. P. Pridham, Tannaka duality for enhanced triangulated categories, arXiv:1309.0637] demonstrates the comparison assuming the existence of the motivic t-stru …
16
votes
DG categories in algebraic geometry - guide to the literature?
There are plenty of interesting dg-categories one can associate to a scheme. From the point of view of six functor yoga, these should be viewed as "categories of coefficients" for cohomology theories …
23
votes
Accepted
Motivation and potential applications of spectral algebraic geometry
This is not really an answer to your question, just an attempt to address your question from the comments.
There are various flavours of homotopical or higher algebraic geometry that are commonly con …
9
votes
Accepted
K theory long exact sequence
Regarding the first question:
If $X$ is quasi-compact quasi-separated and $U \to X$ is a quasi-compact open immersion, then Thomason-Trobaugh showed that there is a "proto-localization sequence", i.e …
8
votes
Accepted
Could we extend the exact sequence $K^0(X)\to K_0(X)\to K_0(D_{sg}(X))\to 0$ to the left?
The exact sequence of triangulated categories
$$ Perf(X)\to D^b_{coh}(X)\to D_{sg}(X) $$
may be lifted to an exact sequence of stable $\infty$-categories or dg-categories in the sense of BGT: choose …
2
votes
Accepted
Integral transform on noncommutative spaces
Let $DGCat_k$ denote the $\infty$-category obtained by localizing the category of dg-categories at Morita equivalences. This is presented by the Morita model structure on the category of dg-categorie …
15
votes
Accepted
What is the applications of the dg-enhancements of derived categories of sheaves
It is hard to know where to begin! A general principle is that as long as you are only concerned with the derived category of a single variety, it is generally sufficient to consider it as a triangul …
6
votes
Accepted
Do algebraic stacks satisfy fpqc descent?
It may be helpful to have a look at these notes by Anatoly Preygel (see also MO/15910/2503). In particular, Proposition 3.3.6 says that an algebraic stack is an fpqc sheaf if the diagonal is quasi-af …