Sharpness conjecture for the Serre-type lower bound in weighted projective spaces

Let P(a0,a1,,am)\mathbb{P}(a_0,a_1,\ldots,a_m) be a weighted projective space over Fq\mathbb{F}_q, let eq(d;1,a1,a2,,am)e_q(d;1,a_1,a_2,\ldots,a_m) be the minimum number of Fq\mathbb{F}_q-rational zeros of a nonzero weighted-homogeneous polynomial of degree dd, and suppose that a0=1a_0=1 and lcm(a1,a2,,am)d\operatorname{lcm}(a_1,a_2,\ldots,a_m)\mid d. Order the weights so that a1a2ama_1\leq a_2\leq\ldots\leq a_m. Sharpness conjecture. The lower bound from the preceding lemma is sharp, namely

eq(d;1,a1,a2,,am)=min{pm,da1qm1+pm2}.e_q(d;1,a_1,a_2,\ldots,a_m)=\min\left\{p_m,\frac{d}{a_1}q^{m-1}+p_{m-2}\right\}.

The conjecture predicts the exact minimum number of rational zeros in this weighted-projective setting under the stated divisibility and weight-ordering assumptions.

Sources & referencesView supporting material

Primary source

Yves Aubry, Wouter Castryck, Sudhir R. Ghorpade, Gilles Lachaud, Michael E. O'Sullivan and Samrith Ram, “Hypersurfaces in weighted projective spaces over finite fields with applications to coding theory”, arXiv:1706.03050 (2017).

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