Grothendieck's standard conjectures

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Let YY be a smooth projective variety of dimension dYd_Y over a field kk, let H∗H^* be a Weil cohomology, and let Halg⁡2j(Y)⊂H2j(Y)H^{2j}_{\operatorname{alg}}(Y) \subset H^{2j}(Y) denote the image of the cycle class map CHj(Y)→H2j(Y)CH^j(Y) \to H^{2j}(Y). For an ample divisor h∈Pic⁡(Y)h \in \operatorname{Pic}(Y), write

Lhj:=⋅hj:Hj(Y)→H2dY−j(Y).L_h^j:=\cdot h^j:H^j(Y)\to H^{2d_Y-j}(Y).

Let δj\delta_j denote the Künneth components of the diagonal in

ΔY∈H2dY(Y×Y)≅⨁j=02dYHj(Y)⊗H2dY−j(Y).\Delta_Y\in H^{2d_Y}(Y\times Y)\cong\bigoplus_{j=0}^{2d_Y}H^j(Y)\otimes H^{2d_Y-j}(Y).

Grothendieck's standard conjectures. The following assertions hold: (1) there exist correspondences Λj∈CHj(Y×Y)\Lambda_j\in CH^j(Y\times Y) such that Λj∗:H2dY−j(Y)→Hj(Y)\Lambda_{j*}:H^{2d_Y-j}(Y)\to H^j(Y) is the inverse of LhjL_h^j; (2) every Künneth component δj\delta_j is induced by an algebraic cycle, equivalently δj∈Halg⁡2dY(Y×Y)\delta_j\in H^{2d_Y}_{\operatorname{alg}}(Y\times Y); and (3), for every γ∈Halg⁡2j(Y)\gamma\in H^{2j}_{\operatorname{alg}}(Y), if γ⋅γ′=0\gamma\cdot\gamma'=0 for all γ′∈Halg⁡2(dY−j)(Y)\gamma'\in H^{2(d_Y-j)}_{\operatorname{alg}}(Y), then γ=0\gamma=0.

These are Grothendieck's standard conjectures: the Lefschetz standard conjecture, the Künneth standard conjecture, and the assertion that numerical and homological equivalence coincide on algebraic cohomology classes. The paper's abstract states that it proves them for the Fano variety of lines on a smooth cubic hypersurface, but the supplied text does not specify which of the assertions is being proved or provide a resolution status for the general formulation.

References

Primary source

Humberto A. Diaz, “The standard conjectures for the variety of lines on a cubic hypersurface”, arXiv:1706.06683 (2017).

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