Conjectural square-root error bound for hyperbolic lattice counting along a geodesic

Let ll be a geodesic, let N(X,l)N(X,l) be the associated hyperbolic lattice counting function, and let

M(X,l):=1/2<sj12πγ1(sj)u^j2XsjM(X,l):=\sum_{1/2<s_j\leq 1}\frac{2}{\pi}\gamma_1(s_j)|\hat{u}_j|^2X^{s_j}

be its main term. Define the error term by

E(X,l):=N(X,l)M(X,l).E(X,l):=N(X,l)-M(X,l).

Square-root error conjecture. For every ϵ>0\epsilon>0,

E(X,l)=O(X1/2+ϵ),E(X,l)=O\big(X^{1/2+\epsilon}\big),

where the estimate depends on ll and ϵ\epsilon. The conjecture is the pointwise analogue of the proved mean-square bound, and would give essentially square-root cancellation in the hyperbolic lattice counting problem along ll; its status is open.

Sources & referencesView supporting material

Primary source

Dimitrios Lekkas and Yiannis Petridis, “A relative trace formula and counting geodesic arcs in the hyperbolic plane”, arXiv:2509.12902 (2025).

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