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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 …
Ali Caglayan's user avatar
  • 1,185
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 …
AAK's user avatar
  • 5,901
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 …
AAK's user avatar
  • 5,901
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' …
AAK's user avatar
  • 5,901
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 …
AAK's user avatar
  • 5,901
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 …
AAK's user avatar
  • 5,901
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 …
AAK's user avatar
  • 5,901
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 …
AAK's user avatar
  • 5,901
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 …
AAK's user avatar
  • 5,901
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 …
AAK's user avatar
  • 5,901
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 …
AAK's user avatar
  • 5,901
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 …
AAK's user avatar
  • 5,901
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 …
AAK's user avatar
  • 5,901
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 …
Community's user avatar
  • 1

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