Vemulapalli's scrollar-invariant polytope conjecture for primitive covers

Let k3k\geq 3, let g0g\geq 0, and consider the polytope

Pk:={xRk1ik1xi=1, 0x1xk1, xi+jxi+xj}.\mathcal P_k:=\left\{\mathbf{x}\in\mathbb R^{k-1}\mid \sum_{i\leq k-1}x_i=1,\ 0\leq x_1\leq\dots\leq x_{k-1},\ x_{i+j}\leq x_i+x_j\right\}.

A scrollar-invariant tuple is a tuple of positive integers e=(e1,,ek1)\mathbf e=(e_1,\dots,e_{k-1}) with e1++ek1=g+k1e_1+\dots+e_{k-1}=g+k-1. Vemulapalli's conjecture. Such a tuple arises as the scrollar invariants of a primitive degree-kk cover π:CPk1\pi:C\rightarrow\mathbb P^1_{\mathbb k} from a genus-gg curve if and only if

(e1g+k1,,e1g+k1)Pd.\left(\frac{e_1}{g+k-1},\dots,\frac{e_1}{g+k-1}\right)\in\mathcal P_d.

The conjecture gives a polyhedral characterization of the scrollar invariants that occur for primitive covers of the projective line. The supplied text attributes it to Vemulapalli and states no evidence of a resolution.

Sources & referencesView supporting material

Primary source

Riccardo Redigolo, “The Scrollar Invariants of Curves Mapping to a Hirzebruch Surface”, arXiv:2602.08902 (2026).

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