Conjecture on extreme Dirichlet L-values in cosets

Let q>1q>1, let X\mathcal{X} be the group of Dirichlet characters modulo qq, and let HXH\leq\mathcal{X} be a subgroup satisfying #Hqε\#H\gg q^\varepsilon. For any coset representative χ0X/H\chi_0\in\mathcal{X}/H, the coset is χ0H\chi_0H. Coset extreme-value conjecture. Every such coset contains an extreme value over the whole group, namely

maxχχ0HL(χ,1/2)=exp((1/2+o(1))logqloglogq).\max\limits_{\chi\in\chi_0H}L(\chi,1/2)=\exp\left((\sqrt{1/2}+o(1))\sqrt{\log q\log\log q}\right).

This extends the Gonek-Hughes-Farmer prediction from the full character group to every sufficiently large subgroup coset. The source presents it as a proposed conjecture and gives no resolution status.

Sources & referencesView supporting material

Primary source

Ivan Ermoshin, “Large central values of Dirichlet L-functions in cosets”, arXiv:2504.05890 (2026).

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