Mixed-syzygy length conjecture for line bundles on the quadric surface

Let X=P1×P1X=\mathbb{P}^1\times\mathbb{P}^1 and let L=aC0+bfL=aC_0+bf. Let δ(a,b)\delta(a,b) denote the length of the region of mixed syzygies. Mixed-syzygy length conjecture. The length is

δ(a,b)=(a1)(b2)=h0(KX+L)gonmax(L)+1.\delta(a,b)=(a-1)(b-2)=h^0(K_X+L)-\operatorname{gon}_{\max}(L)+1.

Equivalently, the highest value pmaxp_{\max} for which LL satisfies Property-(Np)(N_p) is

pmax(a,b)=ab+a+b1(a1)(b2)a=2a+2b3.p_{\max}(a,b)=ab+a+b-1-(a-1)(b-2)-a=2a+2b-3.

This conjecture is proposed for the syzygies of line bundles on P1×P1\mathbb{P}^1\times\mathbb{P}^1, based on the stated examples and the geometry of mixed-weight syzygies.

Sources & referencesView supporting material

Primary source

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

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