Questions tagged [algebraic-k-theory]
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27 questions from the last 365 days
4
votes
2
answers
348
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$K_2$ over finite fields and polynomials over finite fields
I am interested in presentations of the group $SL_n(\mathbb{F}_q)$ (and eventually $SL_n(\mathbb{F}_q[t])$).
The standard "Chevalley" presentation of $SL_n(R)$ for a ring $R$ has generators $...
- 173
2
votes
0
answers
97
views
An injective map in equivariant algebraic K-theory
Let $G$ be a simply connected simple algebraic group over $\mathbb{C}$ and $\mathfrak{g}$ be its Lie algebra. Let $\mathcal{N}$ be the nilpotent cone of $\mathfrak{g}$ consists of all nilpotent ...
- 653
5
votes
0
answers
91
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Relative algebraic $K$ theory of Galois extensions
Let $R$ be a domain, e.g. $\mathbb{Z}$, and let $R\to R[x]/I$ be an integral extension, e.g $\mathbb{Z}[i]$.
Is anything known about the relative algebraic $K$ groups, $K_*(R',R)$? For example, when $...
- 2,907
2
votes
0
answers
114
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The induced map between push outs in an exact infinity category
Let $(\mathcal{C} , \mathcal{M} , \mathcal{E})$ be an exact $\infty$-category. (I am following the definition in Higher Segal Spaces $I$ by Dyckerhoff and Kapranov). Assume that $F$ is a cofiberation ...
- 167
3
votes
1
answer
288
views
Derived Koszul complex
Let $X$ be a projective variety over $\mathbb{C}$ and $V$ be a vector bundle over $X$. Let $\pi: V\to X$ be the natural projection.
Let $i: X\to V$ be the zero section map. Let $V^\vee$ be the dual ...
- 653
2
votes
0
answers
205
views
What role does homotopy play in Karoubi's K-Theory?
In Karoubi's book K-Theory An Introduction, he defines the groups $K^{p,q}(\mathcal{C})$ for a pseudo-abelian Banach category as equivalence classes of triples $(E,F,\alpha)$, where $E,F \in \mathcal{...
- 233
5
votes
0
answers
255
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Necessity of Banach category for K-theory
In Karoubi's book on K-Theory (K-Theory, An Introduction), he introduces the groups $K^{p,q}(C)$ for a pseudo-abelian Banach category $C$.
My question is whether the requirement that $C$ be a Banach ...
- 233
3
votes
0
answers
107
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rational homology of SO(2,1) over number fields
Let $\mathrm{SO}(2,1)$ be the special orthogonal group defined by the quadratic from $q(x,y,z)=x^2+y^2-z^2$.
This is a connected non-simpy connected algebraic group.
Now, let $F$ be a number field, ...
7
votes
1
answer
843
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Algebraic K-theory and Witt groups
Let $S$ be a ring with involution (with 2 invertible). Suppose that the non connective algebraic K-theory $K(S)$ is 0 (i.e. $K_{n}(S)=0$, for all $n$).
Can we say something about the (higher) Witt ...
- 855
3
votes
2
answers
246
views
Explicit description of transfer for $K_1$
Let $R$ be a commutative regular ring and let $s \in R$ be an element such that $R / s$ is also regular. Then we have a long exact localization sequence
$$
\ldots \rightarrow K_i(R/s) \rightarrow K_i(...
4
votes
0
answers
112
views
The $K_1$-group of integer valued polynomials
Let $R=$ Int$(\mathbb{Z}) = \{f \in \mathbb{Q}[x]| f(\mathbb{Z}) \subset \mathbb{Z}\}$. I am interested to find $K_1(R)$. I list my trials below:
Let us construct a Milnor square $$\matrix{R&\...
- 141
14
votes
1
answer
498
views
Abelianization of $\mathrm{GL}_n(\mathbb{Z})$
$\DeclareMathOperator\GL{GL}\DeclareMathOperator\SL{SL}$What is the abelianization of $\GL_n(\mathbb{Z})$? I know the abelianzation of $\GL_n(\mathbb{F})$ where $\mathbb{F}$ is a field and the ...
- 911
5
votes
1
answer
318
views
Surjection onto $H_{2}(\mathrm{PGL}(2,\mathbb{C}),\mathbb{Z})$
Let $G \leq \mathrm{PGL}(2,\mathbb{C})$ be the subgroup of upper-triangular matrices. I am interested in the natural morphism on the Schur multiplier (i.e. group homology as discrete groups)
$H_{2}(G,...
- 305
2
votes
0
answers
108
views
Higher chow groups of affine toric varieties
Let $X$ be an affine toric variety defined over an algebraically closed field $k$ of characteristic zero.
I am trying to use Bloch’s Riemann-Roch Theorem for quasi-projective algebraic schemes in his ...
- 639
5
votes
2
answers
397
views
Ring with vanishing $K_0$
Suppose we have a ring $R$ such that the Grothendieck group $K_{0}(R)=0$.
Question 1: Does it follow that there exists two positive natural numbers $n\neq m$ such that
$R^{m}$ is isomorphic to $ R^{n}$...
- 855
5
votes
3
answers
443
views
Group completion of a monoid (braid groups)
Let $B_n$ be the braid group on $n$ strands, $B_{\infty}$ the direct limit of braid groups.
For a discrete group $G$, we let $BG$ to be the classifying space of $G$.
After reading this question, I was ...
- 140
4
votes
1
answer
328
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Homotopy coherence datum for composition of Becker-Gottlieb transfers
I have a question about certain detail in following answer by Denis Nardin adressing the concept of presheaves with transfer (mostly known in constructions in motivic homotopy theory) from viewpoint ...
- 6,018
2
votes
0
answers
161
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Vanishing differential of Brown-Gersten-Quillen spectral sequence
Let $k$ be an algebraically closed field of characteristic zero and $X$ be an affine, simplicial toric 3-fold over the field $k$. I am trying to use the Brown-Gersten-Quillen spectral sequence to ...
- 639
1
vote
0
answers
153
views
Stable homology of general linear groups
For what class of rings $R$, is the stable homology (with various choices of coefficients) of $GL_n(R)$ known? Borel computed it rationally for number rings, Quillen computed it for finite fields. Are ...
- 965
3
votes
1
answer
244
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Grothendieck group and an almost localization
Let $T$ be a small triangulated category and let $S\subset T$ be a full triangulated subcategory. We denote this embedding by $I: S\rightarrow T$.
Let $F: T\rightarrow S$ be a triangulated functor ...
- 855
4
votes
1
answer
166
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The action of the Grothendieck group on higher K-theory groups
Let $(C,\otimes)$ be a monoidal (non symmetric) Waldhausen category. In particular, under these conditions,
$K_{0}(C)$ is a ring and $K_{i}(C)$ are $K_{0}(C)$-bimodule for any $i\in \mathbb{Z}$.
...
- 855
1
vote
1
answer
127
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Example of triangulated category with vanishing $K_0$
Let $R$ be a ring, let $\operatorname{Perf}(R)$ the category of perfect modules over $R$. Suppose we have $E$ an perfect $R$-module (concentrated in degree $0$) such that its class $[E]\in K_0(R)$ is ...
- 855
6
votes
0
answers
162
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$K_0$ of arithmetic surfaces
In his paper "Algebraic K-Theory and classfield theory of arithmetic surfaces", Annals of Mathematics 114 (1981), Spencer Bloch proved the following result: if $A$ is a finitely generated ...
12
votes
1
answer
429
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Plus construction on Simplicial Sets?
I had asked this question in Math StackExchange a few days ago, but didn't get any answers. I believe its more suitable to be asked here.
Write $\mathsf{sSet}$ for the category of simplicial sets and $...
- 174
1
vote
0
answers
26
views
Coordinate transformation for 3-dimensional simplicial cone in $\mathbb{R}^3$
Let $k$ be an algebraically closed field and let $\sigma$ be a 3-dimensional simplicial cone in $\mathbb{R}^3$.Let $X$ be the affine toric variety over $k$ associated to the cone $\sigma$, i.e. set $X$...
- 639
8
votes
0
answers
123
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The homotopy inverse on Quillen's $S^{-1}S$ construction
Suppose $S$ is a symmetric monoidal groupoid. Take Quillen and Grayson's $S^{-1}S$-construction, which is a symmetric monoidal category with objects given by pairs $(m,n)$ and maps given by ...
- 2,303
2
votes
0
answers
124
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Can K$_3$ of finite fields be related to Teichmüller cocycles?
This is sort of a blind shot, but...
For a ring $R$, its third algebraic K-group is given by $\operatorname K_3(R)=H_3(\operatorname{St}(R))$.
To simplify matters, let $R$ be a finite field $\mathbb ...
- 18.4k