Schur-finiteness in $λ$-rings
We introduce the notion of a Schur-finite element in a $λ$-ring.
math.KT↗
arXiv subjects
C. Weibel
Publications and source records attributed to C. Weibel.
Bass' $NK$ groups and $cdh$-fibrant Hochschild homology
The $K$-theory of a polynomial ring $R[t]$ contains the $K$-theory of $R$ as a summand. For $R$ commutative and containing $\Q$, we describe $K_*(R[t])/K_*(R)$ in terms of Hochschild homology and the cohomology of Kähler differentials for the $cdh$ topology. We use this to address Bass' question, on whether $K_n(R)=K_n(R[t])$ implies $K_n(R)=K_n(R[t_1,t_2])$. The answer is positive over fields of infinite transcendence degree; the companion paper arXiv:1004.3829 provides a counterexample over a number field.
math.KT↗
A negative answer to a question of Bass
In this companion paper to arXiv:0802.1928 we provide an example of an isolated surface singularity $R$ over a number field such that $K_0(R) = K_0(R[t])$ but $K_0(R) \neq K_0(R[t_1,t_2])$. This answers, negatively, a question of Bass.
math.KT↗
Roitman's theorem for singular complex projective surfaces
Let $X$ be a complex projective surface with arbitrary singularities. We construct a generalized Abel--Jacobi map $A_0(X)\to J^2(X)$ and show that it is an isomorphism on torsion subgroups. Here $A_0(X)$ is the appropriate Chow group of smooth 0-cycles of degree 0 on $X$, and $J^2(X)$ is the intermediate Jacobian associated with the mixed Hodge structure on $H^3(X)$. Our result generalizes a theorem of Roitman for smooth surfaces: if $X$ is smooth then the torsion in the usual Chow group $A_0(X)$ is isomorphic to the torsion in the usual Albanese variety $J^2(X)\cong Alb(X)$ by the classical Abel-Jacobi map.
alg-geom↗