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Algebraic and topological K-theory, relations with topology, commutative algebra, and operator algebras

18 votes
1 answer
1k views

Which motivic cohomology groups of complex numbers are non-torsion?

I would like to know which motivic cohomology groups of complex numbers are non-zero and ("better") non-torsion, i.e., for which $(i,j)$ the $i$th cohomology of the complex ${\mathbb{Q}}(j)$ over $\ma …
Mikhail Bondarko's user avatar
14 votes
1 answer
1k views

Motivic cohomology vs. K-theory for singular varieties

As far as I understand, for a smooth variety $X$ its motivic cohomology could be described as the corresponding piece of the $\gamma$-filtration of (Quillen's) $K^*(X)$; this is completely true for $\ …
Mikhail Bondarko's user avatar
9 votes
1 answer
918 views

The vanishing of non-connective K-theory in negative degrees

In the works of Cisinski, Tabuada, and Schlichting certain non-connective K-theory groups for a differential graded category $C$ are defined. As far as I understand, $K_i(C)$ is not necessarily zero f …
Mikhail Bondarko's user avatar
8 votes
1 answer
424 views

When does the continuous Galois(=etale) cohomology of fields coincide with the naive one? Of...

For a field $F$ I am interested in its $l$-adic (Galois=\'etale) cohomology; here $l$ is a prime distinct from the characteristic of $F$ (for simplicity one may assume that the latter is $0$). For $ …
Mikhail Bondarko's user avatar
8 votes
1 answer
565 views

Continuity of l-adic cohomology: is the cohomology of the generic point isomorphic to the co...

Let $X$ be a variety over an algebraically closed field $k$. Denote by $\eta$ its generic point; it is the inverse limit of the open subvarieties $X_i$ of $X$. It is well known that the etale cohomolo …
Mikhail Bondarko's user avatar
7 votes
0 answers
265 views

Do there exist "non-algebraic tensor products" for "algebraic" triangulated categories?

Let us call a triangulated category algebraic if it admits a differential graded enhancement (i.e., an enrichment in complexes of abelian groups). Certainly, there is a notion of a tensor product on d …
Mikhail Bondarko's user avatar
7 votes
0 answers
376 views

K-theory of the infinite dimensional projective space

What is the $K$-theory of the category of coherent sheaves on the infinite (countable) dimensional projective space over a field? As far as I know, $K$-theory is oriented; hence this theory should be …
Mikhail Bondarko's user avatar
6 votes
1 answer
240 views

For which exact couples do associated spectral sequences degenerate at $E_1$?

It is well known that a bigraded exact couple of objects of an abelian category yields a spectral sequence (cf. https://ncatlab.org/nlab/show/exact+couple#SpectralSequencesFromExactCouples). My questi …
Mikhail Bondarko's user avatar
6 votes
0 answers
241 views

Are Tate twists of t-positive motives positive with respect to the Voevodsky's homotopy t-st...

Let $X$ be a Voevodsky's motif (over a perfect field) that belongs to the positive part of the homotopy $t$-structure (i.e. its cohomology as an object of $D^-(ShSmCor)$ is zero in negative degrees). …
Mikhail Bondarko's user avatar
6 votes
0 answers
136 views

Comparison of K-groups of (affine) singular schemes with K'=G-groups

It is well known that Quillen K-theory coincides with $K'=G$-theory for regular schemes, and can be distinct from it for singular ones. Are there any methods for studying this distinctions? In particu …
Mikhail Bondarko's user avatar
6 votes
1 answer
617 views

On various "extension closures" and "orthogonals" in triangulated categories

A vague form of my question is the following one: for a class of objects $D$ of a triangulated category $C$ we consider the class $E$ of objects that satisfy $Mor_{C}(d,e)=\{0\}\ \forall d\in D$; whi …
Mikhail Bondarko's user avatar
6 votes
1 answer
237 views

Left orthogonals to compact objects in triangulated categories: existence and "control"?

Let $C$ be a compactly generated triangulated category. Can it contain a non-zero object $M$ such that there are no non-zero morphisms FROM $M$ into compact objects? I would be grateful for any exampl …
Mikhail Bondarko's user avatar
6 votes
0 answers
102 views

On K-theory of blow-ups of compact complex manifolds

Is there a long exact sequence for the K-theory of (coherent sheaves on) blow-ups of compact complex manifolds? Does it split? What can one say on (possibly, singular) complex analytic spaces here? …
Mikhail Bondarko's user avatar
5 votes
1 answer
318 views

Is the motivic homotopy spectrum of Hermitian K-theory $\eta$-complete?

Theorem 1.2 of the paper "The motivic Hopf map solves the homotopy limit problem for K-theory" (see https://elibm.org/article/10011880) says that (under certain assumptions on the base field) the homo …
Mikhail Bondarko's user avatar
5 votes
0 answers
186 views

Which t-structure extend from subcategories of compact objects uniquely?

Let $T$ be a compactly generated triangulated category, that is, $T$ is closed with respect to small coproducts and equals its own smallest triangulated subcategory closed with respect to coproducts a …
Mikhail Bondarko's user avatar

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