7
votes
1answer
225 views
Waldhausen $K$-theory for $G$-spaces
I would guess that the following is true, and that somebody has worked it out, but I don't recall ever seeing it. Can anyone point me to any literature on it?
Let $G$ be a finite …
24
votes
2answers
656 views
What arithmetic information is contained in the algebraic K-theory of the integers
I'm always looking for applications of homotopy theory to other fields, mostly as a way to make my talks more interesting or to motivate the field to non-specialists. It seems like …
10
votes
2answers
282 views
What is the Q-construction, metaphysically?
An exact (small) category $P$ is an environment in which we make sense of the "put-together"-edness of objects via (short) exact sequences. It seems like the K-theory of an exact c …
4
votes
2answers
260 views
K-theory of monoidal categories
I am novice in the algebraic K- theory and don' t know if this is the right place for the following questions. So some people might consider them as basic questions.
Consider an e …
0
votes
0answers
128 views
A question about higher K-theory
Suppose $\mathcal{A,B,C}$ are additive categories, $\mathcal B$ is a subcategory of $\mathcal C$. Now let $F,G: \mathcal A\rightarrow\mathcal B$ be two additive functors. Suppose $ …
8
votes
1answer
292 views
Motivic cohomology and cohomology of Milnor K-theory sheaf
Let $X$ be a smooth variety over a field $k$. (Assume $k$ has characteristic 0 if it helps; in fact I'd be happy to assume that $k$ is a finite extension of either $\mathbf{Q}$ or …
2
votes
1answer
334 views
Intuition as to why the K-theory of a ring should be the homotopy theory of an H-space
For an ideal $I \subset R$ with relative K-groups $K_i(R,I)$ we have an exact sequence
$K_2(R) \to K_2(R,I) \to K_2(R/I) \to K_1(R) \to K_1(R,I) \to K_1(R/I)$
$\to K_0(R) \to K_0 …
8
votes
2answers
235 views
Categorical description of the second K-group
Let $\mathcal{P}$ be a (small) exact category. Without delving into any homotopy theory, we can provide characterisations of $K_0(\mathcal{P})$ and $K_1(\mathcal{P})$ as plain cate …
1
vote
1answer
100 views
homology of $B S^{-1} S$ computation in the proof that $+ = Q$
Let $S$ denote the category of projective (left) $R$-modules with isomorphisms for arrows. We have that
$BS^{-1}S \sim B \text{GL}(R)^+ \times K_0(R)$
In proving this, in Sri …
3
votes
2answers
289 views
Morphisms between $K_0$
I suppose this is a question with a well known answer. Suppose $A$ and $B$ are two algebras over some field and there is a map
$$
f: \operatorname{K_0}(A) \to \operatorname{K_0}(B …
9
votes
3answers
496 views
Plus construction considerations.
In order to realise the K-groups of a ring as the homotopy groups of some space associated to that ring, Quillen proposed the following (roughly-sketched) construction:
Recall tha …
1
vote
1answer
170 views
Path components of a monoidal category form a monoid?
In Grayson's 'Higher Algebraic K-theory II', leading up to the categorical generalisation of the plus construction, he considers $\pi_0(S) = \pi_0(BS)$, where $S$ is a (small, symm …
1
vote
1answer
168 views
Simplicial sets from bisimplicial sets, and their realisations.
From a bisimplicial space $T$, one can consider the simplicial spaces $\underline p \mapsto T_{pp} $, $\underline p \mapsto |\underline q \mapsto T_{pq} |$, and $\underline q \maps …
20
votes
1answer
579 views
Is every ‘'group-completion’' map an acyclic map?
I start with a longer discussion which will result in a precise version of the question. A am puzzled about an issue with the
Quillen plus construction. I have seen outstanding ex …
9
votes
0answers
211 views
Geometrizing the Third Cohomology of a Complex Lie Group
If $G_\mathbb{C}$ is a simply-connected simple complex Lie group, theorem 5.4.10 of Brylinski's "Loop Spaces, Characteristic Classes, and Geometric Quantization" claims that there …

