The rationality conjecture for cubic fourfolds with associated K3 surfaces

From papers

Let XX be a smooth cubic fourfold in P5\mathbf{P}^5. Let A(X)=H4(X,Z)H2,2(X)A(X)=H^4(X,\mathbf{Z})\cap H^{2,2}(X), and let Cd\mathcal{C}_d denote the Hassett divisor of special cubic fourfolds with a labelled discriminant-dd rank-two lattice. The numerical condition (*) is

d>6andd is not divisible by 4,9, or by a prime p2(mod3).d>6\quad\text{and}\quad d\text{ is not divisible by }4,9\text{, or by a prime }p\equiv 2\pmod{3}.

Rationality conjecture. A smooth cubic fourfold XX is rational if and only if XCdX\in\mathcal{C}_d for some dd satisfying (*).

This is the rationality criterion suggested by the relationship between special cubic fourfolds and associated K3 surfaces. The source gives no resolution status for this assertion.

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Sources & referencesView supporting material

Primary source

Claudio Pedrini, “K3 surfaces associated to a cubic fourfold”, arXiv:2405.05074 (2024).

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