Prefix sum recurrence conjecture for Legendre-symbol walks

Let pp be a prime and let χ\chi be the Legendre symbol modulo pp. For aFpa\in\mathbb{F}_p and t{0,1,,p1}t\in\{0,1,\ldots,p-1\}, define the prefix sum

Ψ(a,t)=j=0tχ(a+j).\Psi(a,t)=\sum_{j=0}^{t}\chi(a+j).

Prefix sum recurrence conjecture. For an absolute constant A>0A>0, independently of aFpa\in\mathbb{F}_p,

{t:Ψ(a,t)=0}=O(p(logp)A).\left|\{t:\Psi(a,t)=0\}\right|=O\left(\sqrt{p}(\log p)^A\right).

A stronger related question asks whether, for some absolute constant A>0A>0,

maxhZ{0tp1:Ψ(0,t)=h}=O(p(logp)A).\max_{h\in\mathbb{Z}}\left|\left\{0\leq t\leq p-1:\Psi(0,t)=h\right\}\right|=O\left(\sqrt{p}(\log p)^A\right).

These estimates would control how often the Legendre-symbol prefix-sum walk attains a given value, and hence the frequency of intersection numbers in the associated projective-plane construction. The stated status of these bounds is unknown.

Sources & referencesView supporting material

Primary source

Zoltán Lóránt Nagy and Zsuzsa Weiner, “Balanced intersection size distributions in projective planes”, arXiv:2605.23644 (2026).

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