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

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=w0w1w2wn1=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,dw1qn1+pn2}.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 dw1(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.

Sources & referencesView supporting material

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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