The Two Conjecture for quadratic Dirichlet characters

From papers

Let χ1\chi_1 and χ2\chi_2 be nontrivial, primitive Dirichlet characters modulo q1q_1 and q2q_2, respectively, with χ1χ2(1)=1\chi_1\chi_2(-1)=1. Let Sχ1,χ2S_{\chi_1,\chi_2} be their generalized Dedekind sum, and let Γ1(q1q2)\Gamma_1(q_1q_2) be the congruence subgroup appearing in its image. The Two Conjecture. If χ1\chi_1 and χ2\chi_2 are quadratic, then

Sχ1,χ2(Γ1(q1q2))=2Z.S_{\chi_1,\chi_2}(\Gamma_1(q_1q_2))=2\mathbb{Z}.

The conjecture concerns the image of the newform Dedekind sum, which is known to be a full-rank lattice in the number field generated by the character values. The paper presents partial progress toward the containment in 2Z2\mathbb{Z}, but the equality remains open in the supplied source.

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Sources & referencesView supporting material

Primary source

Evelyne S. Knight, Carlos Alexov Matos, Amira Sefidi and Matthew P. Young, “The image of the generalized Dedekind sum”, arXiv:2503.09741 (2025).

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