MathOverflow is a question and answer site for professional mathematicians. Join them; it only takes a minute:

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

I would like to study the cohomology of the Henselization $H_X(Z)$ of a closed subvariety $Z$ of a variety $X$. I would like the following facts to be true (and to make sense!:)).

a.) The motivic cohomology of $Z$ with finite coefficients (prime to the base field characteristic) is isomorphic to that of $H_X(Z)$; cf. On motivic cohomology with compact support b.) For the natural morphism $f:Z\to H_X(Z)$ I would like $Rf_\ast f^\ast$ to be isomorphic to the identity functor on a certain triangulated category of 'nice' (constructible??) complexes of etale sheaves $H_X(Z)$. I would not like to assume that $X$ is affine or that $Z$ is smooth (in particular, I need $Z$ being a smooth normal crossing divisor).

So, I have several questions.

  1. Could the statements above be true; what additional restrictions are needed?
  2. Which references could help me?
  3. What could be the plan in order to deduce the statements I need from the known facts? What are the main difficulties? In particular, (as far as I understand) Henselizations are 'very far from being of finite type' (in the non-affine situation). So, in order to define the cohomology of $H_X(Z)$ I should pass to certain limits and sheafify? How does one usually study $f^\ast$ and $Rf_\ast$ in such an 'infinite' setting?
  4. Actually, I would be satisfied by any sort of 'algebraic tubular neigbourhood' of $Z$ in $X$ such that a.) and b.) hold (and make sense!!) for it. Is the henselization more appropriate than other existing constructions here?
share|cite|improve this question

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Browse other questions tagged or ask your own question.