The algebraic cohomology exactness conjecture for resolutions

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Let XX be a singular projective variety, let ϕ:X~→X\phi:\widetilde{X}\to X be any resolution of singularities, and let EE be the exceptional divisor. Let pp be an integer such that

dim⁡(Xsing)≤p−1.\operatorname{dim}(X_{\mathrm{sing}})\le p-1.

The cohomology sequence

H2p(X)→H2p(X~)→H2p(E)H^{2p}(X)\to H^{2p}(\widetilde{X})\to H^{2p}(E)

is exact. The algebraic cohomology exactness conjecture. Taking algebraic cohomology groups preserves this exactness; namely,

HA2p(X)→HA2p(X~)→HA2p(E)H^{2p}_A(X)\to H^{2p}_A(\widetilde{X})\to H^{2p}_A(E)

is exact. This conjecture asks whether exactness survives after restricting to algebraic cohomology classes; the source does not specify whether it has been resolved.

References

Primary source

Ananyo Dan and Inder Kaur, “Mumford Tate groups and the Hodge conjecture”, arXiv:2301.01005 (2023).

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