Scholl's integral-part conjecture for motivic extensions

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Let FpF_{\mathfrak p} be a local field, let Mp=hi−1(X)(n)M_{\mathfrak p}=h^{i-1}(X)(n) for a smooth projective variety XX over FpF_{\mathfrak p} and integers n,i≥1n,i\geq1, and suppose that XX has a regular model X\mathcal X over Op\mathcal O_{\mathfrak p}. Define Ext⁡Op1(1,Mp)\operatorname{Ext}^1_{\mathcal O_{\mathfrak p}}(\mathbb{1},M_{\mathfrak p}) as the inverse image, under the expected KK-theoretic isomorphism, of the image of (K2n−i(X)⊗ZQ)(n)(K_{2n-i}(\mathcal X)\otimes_{\mathbb Z}\mathbb Q)^{(n)} in (K2n−i(X)⊗ZQ)(n)(K_{2n-i}(X)\otimes_{\mathbb Z}\mathbb Q)^{(n)}. Let Ext⁡good1(1,Mp)ℓ\operatorname{Ext}^1_{\mathrm{good}}(\mathbb{1},M_{\mathfrak p})_\ell denote the subspace of extensions having good reduction.

Integral-part conjecture. For any prime ℓ\ell not lying below p\mathfrak p,

Ext⁡Op1(1,Mp)=Ext⁡good1(1,Mp)ℓ.\operatorname{Ext}^1_{\mathcal O_{\mathfrak p}}(\mathbb{1},M_{\mathfrak p})=\operatorname{Ext}^1_{\mathrm{good}}(\mathbb{1},M_{\mathfrak p})_\ell.

This conjecture identifies the KK-theoretic and realization-theoretic definitions of the local integral part of motivic cohomology and supersedes the preceding independence assertion.

References

Primary source

Quentin Gazda, “On the Integral Part of A-Motivic Cohomology”, arXiv:2201.09304 (2024).

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