On motivic cohomology of commutative C*-algebras

Abstract

Consider the ring of complex-valued continuous functions on a compact Hausdorff space $X$. Cortiñas--Thom computed its nonpositive algebraic $K$-theory, confirming Rosenberg's expectation. We give a motivic refinement of their result: For $i\geq 2j\geq 0$, the $i$th integral motivic cohomology group of weight $j$ is naturally isomorphic to the $i$th Betti cohomology group of $X$.