Nori's conjecture for Chow groups of a general hypersurface

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Let XX be a smooth projective variety, let LL be a very ample line bundle on XX, and let S=P(H0(X,Ln)∗)S=\mathbb{P}(H^0(X,L^n)^*) parametrize hypersurfaces defined by sections of LnL^n. Write KK for the function field of SS, let K‾\overline{K} be its algebraic closure, and let YK⊂XK=X×Spec⁡(K)\mathcal{Y}_K\subset\mathcal{X}_K=X\times\operatorname{Spec}(K) be the generic hypersurface. The inclusion induces a restriction map on Chow groups.

Nori's conjecture. If nn is sufficiently large, then the natural map

CHi(XK‾)⊗Q⟶CHi(YK‾)⊗QCH^i(\mathcal{X}_{\overline{K}})\otimes\mathbb{Q}\longrightarrow CH^i(\mathcal{Y}_{\overline{K}})\otimes\mathbb{Q}

is an isomorphism for i<dim⁡(YK)i<\dim(\mathcal{Y}_K) and an inclusion for i=dim⁡(YK)i=\dim(\mathcal{Y}_K).

The conjecture predicts that, in the indicated codimensions, a sufficiently general high-degree hypersurface acquires no new rational Chow classes beyond those coming from the ambient variety, with the boundary codimension allowing injectivity rather than surjectivity.

References

Primary source

Kirti Joshi, “A General Noether-Lefschetz Theorem and applications”, arXiv:alg-geom/9305001 (1993).

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