Nori's conjecture for Chow groups of a general hypersurface

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 YKXK=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)QCHi(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.

Sources & referencesView supporting material

Primary source

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

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