Bloch's formula

In algebraic K-theory, a branch of mathematics, Bloch's formula, introduced by Spencer Bloch for ${\displaystyle K_{2}}$, states that the Chow group of a smooth variety X over a field is isomorphic to the cohomology of X with coefficients in the K-theory of the structure sheaf ${\displaystyle {\mathcal {O}}_{X}}$; that is,

${\displaystyle \operatorname {CH} ^{q}(X)=\operatorname {H} ^{q}(X,K_{q}({\mathcal {O}}_{X}))}$

where the right-hand side is the sheaf cohomology; ${\displaystyle K_{q}({\mathcal {O}}_{X})}$ is the sheaf associated to the presheaf ${\displaystyle U\mapsto K_{q}(U)}$, U Zariski open subsets of X. The general case is due to Quillen.^[1] For q = 1, one recovers ${\displaystyle \operatorname {Pic} (X)=H^{1}(X,{\mathcal {O}}_{X}^{*})}$. (see also Picard group.)

The formula for the mixed characteristic is still open.

See also

• Additive K-theory