Let $M$ be a manifold of dimension $n$. It is well-known that there is a perfect intersection pairing $$H_k(M;\mathbb{Z})_{torsion\,\,free}\otimes H_{n-k}(M;\mathbb{Z})_{torsion\,\,free}\rightarrow \mathbb{Z},$$ but there is also a perfect linking pairing $$H_k(M;\mathbb{Z})_{torsion}\otimes H_{n-k-1}(M;\mathbb{Z})_{torsion}\rightarrow \mathbb{Q}/\mathbb{Z}.$$ Is there an algebraic geometry analogue? For instance, etale cohomology is first defined over $\mathbb{Z}_\ell$ then tensored with $\mathbb{Q}_\ell$. It seems plausible that the "right definition" of $\ell$-adic etale cohomology would have $\ell$-torsion and that there would be a linking pairing on the torsion part. The same question applies for crystalline cohomology, or for any Weil cohomology theory. Or is this a feature unique to singular cohomology?
Is there an analogue of the linking pairing in etale, crystalline, etc cohomology theories?
Philip Engel
- 1.5k
- 9
- 12