Directional maximum conjecture for logarithmic derivatives of Dirichlet LL-functions

Let qq tend to infinity through the primes. For a prime qq, let χ0\chi_0 denote the principal character modulo qq, and let L(s,χ)L(s,\chi) be the Dirichlet LL-function associated with a character χ\chi modulo qq. For θ[0,2π]\theta\in[0,2\pi] and σ[12,1]\sigma\in[\frac12,1], consider the maximum over nonprincipal characters χχ0\chi\neq\chi_0. Directional maximum conjecture. As prime qq\to\infty,

maxχχ0χ (modq)Re(eiθLL(σ,χ))maxχχ0χ (modq)L(σ,χ)maxχχ0χ (modq)L(σ,χ),\max_{\substack{\chi\neq\chi_0\\ \chi\ (\operatorname{mod} q)}} \operatorname{Re}\left(e^{-\mathrm{i}\theta}\frac{L'}{L}(\sigma,\chi)\right)\sim \frac{\displaystyle\max_{\substack{\chi\neq\chi_0\\ \chi\ (\operatorname{mod} q)}}|L'(\sigma,\chi)|}{\displaystyle\max_{\substack{\chi\neq\chi_0\\ \chi\ (\operatorname{mod} q)}}|L(\sigma,\chi)|},

uniformly for all θ[0,2π]\theta\in[0,2\pi] and all σ[12,1]\sigma\in[\frac12,1]. This predicts that the largest directional real part of the logarithmic derivative is asymptotic to the ratio of the separate largest derivative and function values; the source motivates it using simultaneous control of prime phases and the belief that central LL-values do not vanish, but no resolution is given.

Sources & referencesView supporting material

Primary source

Daodao Yang, “Omega theorems for logarithmic derivatives of zeta and L-functions”, arXiv:2311.16371 (2023).

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