Saito's conjecture on cohomological characteristic classes

From papers

Let kk be a perfect field, let XX be a closed subscheme of a smooth scheme over kk, and let Λ\Lambda be the finite local coefficient ring in the setup. Let F\mathcal F be a constructible complex of Λ\Lambda-modules of finite tor-dimension on XX. Write ccX,0(F)CH0(X)cc_{X,0}(\mathcal F)\in {\rm CH}_0(X) for the characteristic class defined via the characteristic cycle, and set ccX(F):=ccX,0(F)cc_X(\mathcal F):=cc_{X,0}(\mathcal F). The cohomological characteristic class is CX/k(F)H0(X,KX/k)C_{X/k}(\mathcal F)\in H^0(X,\mathcal K_{X/k}), where KX/k=Rh!Λ\mathcal K_{X/k}=Rh^!\Lambda for the structural morphism h:XSpeckh:X\to {\rm Spec}k. Saito's conjecture. One has

CX/k(F)=cl(ccX(F))inH0(X,KX/k),C_{X/k}(\mathcal F)={\rm cl}(cc_X(\mathcal F))\quad\text{in}\quad H^0(X,\mathcal K_{X/k}),

where cl:CH0(X)H0(X,KX/k){\rm cl}:{\rm CH}_0(X)\to H^0(X,\mathcal K_{X/k}) is the cycle class map. This conjecture asserts that the cohomological characteristic class can be computed from the characteristic cycle; the paper confirms it in the quasi-projective case, while the general case is the broader assertion attributed to Saito.

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Sources & referencesView supporting material

Primary source

Enlin Yang and Yigeng Zhao, “Cohomological Milnor formula and Saito's conjecture on characteristic classes”, arXiv:2209.11086 (2025).

Additional references

2 papers in this index state this conjecture (2017–2022). The statement above is taken from the most recent of them; the others are arXiv:1701.02841.

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