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5 votes

$K_0$ of Burnside ring?

As $AG$ is noetherian of dimension 1*, finitely-generated projective $AG$-modules are classified by their rank and determinant, and so $$K_0(AG) = \mathbb{Z} \oplus Pic(AG).$$ Proposition 10.3.8 of to …
Oscar Randal-Williams's user avatar
4 votes
Accepted

Stable homology of arithmetic groups

The algebraic K-groups of Z are to the homology of SLn(Z) as the Hermitian K-groups of Z are to the homology of Sp2g(Z). There is a paper by Berrick and Karoubi here in which they discuss, and make so …
Oscar Randal-Williams's user avatar
14 votes
Accepted

Can topological cyclic homology compute Picard groups?

Warning: I know nothing about this subject, but found the question interesting so decided to learn something about it. Approach the following with caution. Consider the ring of integers $\mathbb{Z}[\ …
Oscar Randal-Williams's user avatar
17 votes
Accepted

K(F_1) = sphere spectrum?

I understand that this is because GLn(F1) is supposed to be Sigman, the symmetric group on n letters. Thus K(F1) = K(finite sets) which is the sphere spectrum by the Barratt-Priddy-Quillen-Segal theor …
Oscar Randal-Williams's user avatar
13 votes
Accepted

Fundamental theorem of K-theory for loop groups over $\mathbb{F}_1$?

Let $G_n := W(\tilde{A}_{n-1})$. If I understand your description correctly, there is an extension $$1 \to G_n \to S_{n} \wr \mathbb{Z} \overset{sum}\to \mathbb{Z} \to 1$$ and so a $\mathbb{Z}$-Galois …
Oscar Randal-Williams's user avatar
10 votes
Accepted

Homological stability and Waldhausen A-theory

I don't think that you can deduce homological stability of the coinvariants from the Serre spectral sequence as you suggest. But this precise situation was studied in my paper "An upper bound for the …
Oscar Randal-Williams's user avatar
10 votes
Accepted

How can I detect the homology image of a unipotent group in the general linear group?

Suppose first that $F$ is a finite field of characteristic $p$. Then $U_n(F)$ is a Sylow $p$-subgroup of $GL_n(F)$, and so using the transfer in group homology one sees that the image of $f_k$ (for $k …
Oscar Randal-Williams's user avatar
18 votes
Accepted

Is every ''group-completion'' map an acyclic map?

I think I have been able to reproduce the "argument by Wagoner" (perhaps it was removed from the published version?). It certainly holds in more generality that what I have written below, using the no …
Oscar Randal-Williams's user avatar
3 votes
Accepted

Group completion of a monoid (braid groups)

This is explained in my paper "Group-Completion", local coefficient systems, and perfection, Q. J. Math. (Quillen Memorial Issue) 64 (3) (2013) 795-803. A sufficient condition is for the monoid to be …
Oscar Randal-Williams's user avatar