Quasi-FF-splitting of general fibers with trivial relative canonical divisor

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Let π ⁣:X→Y\pi \colon X \to Y be a fiber space of normal varieties. The relative canonical divisor is trivial if KX−π∗KYK_X-\pi^*K_Y is linearly equivalent to zero, and XX is quasi-FF-split when it satisfies the quasi-FF-splitting condition defined in the paper.

General-fiber quasi-FF-splitting conjecture. If the relative canonical divisor is trivial and XX is quasi-FF-split, then a general fiber of π\pi is quasi-FF-split.

The assumption that the generic fiber is a complete intersection in the preceding corollary is technical, motivating this conjecture. It is disproved in general when the relative canonical divisor is anti-ample, as shown by the paper's wild conic bundle example; the stated trivial-divisor case is therefore not supported as an open conjecture by the supplied status evidence.

References

Primary source

Tatsuro Kawakami, Teppei Takamatsu and Shou Yoshikawa, “Fedder type criteria for quasi-F-splitting I”, arXiv:2204.10076 (2025).

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