Aubry et al.'s point-count conjecture for weighted hypersurfaces

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Let k=Fqk=\mathbb{F}_q be a finite field, let Pwn\mathbb{P}_{\mathbf{w}}^n be weighted projective space with weights w=(w0,w1,…,wn)\mathbf{w}=(w_0,w_1,\ldots,w_n), and write

pn=qn+⋯+q+1.p_n=q^n+\cdots+q+1.

For a weighted homogeneous polynomial FF of degree dd, define

eq(d;w0,w1,…,wn)=max⁡{∣X(Fq)∣:X=V(F)}.e_q(d;w_0,w_1,\ldots,w_n)=\max\{|X(\mathbb{F}_q)|:X=V(F)\}.

Aubry et al.'s point-count conjecture. If 1=w0≤w1≤w2≤⋯≤wn1=w_0\leq w_1\leq w_2\leq\cdots\leq w_n and lcm⁡(w1,w2,…,wn)∣d\operatorname{lcm}(w_1,w_2,\ldots,w_n)\mid d, then

eq(d;w0,w1,…,wn)=min⁡{pn,dw1qn−1+pn−2}.e_q(d;w_0,w_1,\ldots,w_n)=\min\left\{p_n,\frac{d}{w_1}q^{n-1}+p_{n-2}\right\}.

It is enough to prove the assertion for d≤w1(q+1)d\leq w_1(q+1), and it is known for weighted projective spaces of dimensions one and two in the cases stated in the source.

References

Primary source

Elira Shaska, Jorge Mello, Sajad Salami and Tony Shaska, “Rational Points and Zeta Functions of Humbert Surfaces with Square Discriminant”, arXiv:2504.19268 (2025).

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