Mixed-syzygy length conjecture for rational surfaces

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Let XX be a rational surface and let LL be an ample and base point free line bundle on XX. Suppose that ∣L∣|L| is a linear system containing curves CC of genus g≥1g\geq 1, and write gon⁡max⁡(L)\operatorname{gon}_{\max}(L) for the maximal gonality among smooth curves in ∣L∣|L|. If

(−KX⋅L)≥gon⁡max⁡(L)+2,(-K_X\cdot L)\geq \operatorname{gon}_{\max}(L)+2,

then δ(L)\delta(L) denotes the length of the region of syzygies of mixed weights. Mixed-syzygy length conjecture. One has

δ(L)=h0(KX+L)−gon⁡max⁡(L)+1.\delta(L)=h^0(K_X+L)-\operatorname{gon}_{\max}(L)+1.

The conjecture is motivated by examples for rational surfaces and describes the mixed-weight part of the syzygy resolution in terms of adjoint sections and maximal gonality.

References

Primary source

Debjit Basu, “Vanishing of weight one syzygies of projective varieties”, arXiv:2511.12994 (2025).

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