The converse Hasse–Witt rank conjecture for curves in characteristic 2

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Let kk be a perfect field of characteristic 22, let Δ\Delta be a two-dimensional lattice polygon satisfying the conditions from Lemma~, and let ff be a Δ\Delta-non-degenerate (or Δ\Delta-toric) Laurent polynomial. Write Cf′C'_f for the associated curve, gg for its genus, and ρ\rho for the quantity defined in the preceding results. For each solution (i0,j0)∈Δ∩Z2(i_0,j_0)\in\Delta\cap\mathbf{Z}^2 of the system of congruences in, let ci0,j0c_{i_0,j_0} denote the corresponding coefficient of ff. Converse Hasse–Witt rank conjecture. The rank of the Hasse–Witt matrix of Cf′C'_f is at least g−ρg-\rho, and this bound is attained if and only if ci0,j0=0c_{i_0,j_0}=0 for every such solution (i0,j0)(i_0,j_0). This conjectured converse would give a geometric interpretation of the stated condition on the coefficients, complementing the proved implication from the coefficient condition to the Hasse–Witt rank bound.

References

Primary source

Wouter Castryck, Marco Streng and Damiano Testa, “Curves in characteristic 2 with non-trivial 2-torsion”, arXiv:1402.3241 (2020).

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