${\mathbb{A}}^1$-connectivity on Chow monoids v.s. rational equivalence of algebraic cycles

Abstract

Let $k$ be a field of characteristic zero, and let $X$ be a projective variety embedded into a projective space over $k$. For two natural numbers $r$ and $d$ let $C_{r,d}(X)$ be the Chow scheme parametrizing effective cycles of dimension $r$ and degree $d$ on the variety $X$. An effective $r$-cycle of minimal degree on $X$ gives rise to a chain of embeddings of $C_{r,d}(X)$ into $C_{r,d+1}(X)$, whose colimit is the connective Chow monoid $C_r^{\infty }(X)$ of $r$-cycles on $X$. Let $B{C}_r^{\infty }(X)$ be the motivic classifying space of this monoid. In the paper we establish an isomorphism between the Chow group $C{H}_r(X{)}_0$ of degree $0$ dimension $r$ algebraic cycles modulo rational equivalence on $X$, and the group of sections of the sheaf of ${\mathbb{A}}^1$-path connected components of the loop space of $B{C}_r^{\infty }(X)$ at $Spec(k)$. Equivalently, $C{H}_r(X{)}_0$ is isomorphic to the group of sections of the $S^1\wedge {\mathbb{A}}^1$-fundamental group ${\Pi }_1^{S^1\wedge {\mathbb{A}}^1}(B{C}_r^{\infty }(X))$ at $Spec(k)$.

25 pages

References in corpus (2)

• Model Structures on Commutative Monoids in General Model Categories
• Admissibility and rectification of colored symmetric operads