Critical-limit conjecture for random multiplicative functions

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Let α(n)\alpha(n) be the random completely multiplicative function appearing in the paper, let μ\mu be the Möbius function, and let mx,∞m_{x,\infty} be the random measure defined in the paper. For f∈{1,μ}f\in\{\mathbf{1},\mu\}, define

V∞critical:=lim⁡x→∞12π∫Rlog⁡log⁡x mx,∞(ds)∣12+is∣2=12π∫Rm∞critical(ds)∣12+is∣2,V_\infty^{\mathrm{critical}}:=\lim_{x\to\infty}\frac{1}{2\pi}\int_{\mathbb{R}}\frac{\sqrt{\log\log x}\,m_{x,\infty}(ds)}{|\frac12+is|^2}=\frac{1}{2\pi}\int_{\mathbb{R}}\frac{m_\infty^{\mathrm{critical}}(ds)}{|\frac12+is|^2},

where m∞critical(ds):=lim⁡x→∞log⁡log⁡x mx,∞(ds)m_\infty^{\mathrm{critical}}(ds):=\lim_{x\to\infty}\sqrt{\log\log x}\,m_{x,\infty}(ds) and all limits are in probability. Critical-limit conjecture. The random variable V∞criticalV_\infty^{\mathrm{critical}} is almost surely finite and strictly positive, and, independently of G∼NC(0,1)G\sim\mathcal{N}_{\mathbb{C}}(0,1),

(log⁡log⁡x)1/4x∑n≤xα(n)f(n)→x→∞dV∞critical G.\frac{(\log\log x)^{1/4}}{\sqrt{x}}\sum_{n\leq x}\alpha(n)f(n)\xrightarrow[x\to\infty]{d}\sqrt{V_\infty^{\mathrm{critical}}}\,G.

The convergence is stable, and for every fixed q∈[0,1)q\in[0,1),

lim⁡x→∞E[∣(log⁡log⁡x)1/4x∑n≤xα(n)f(n)∣2q]=Γ(1+q)E[(V∞critical)q].\lim_{x\to\infty}\mathbb{E}\left[\left|\frac{(\log\log x)^{1/4}}{\sqrt{x}}\sum_{n\leq x}\alpha(n)f(n)\right|^{2q}\right]=\Gamma(1+q)\mathbb{E}\left[\left(V_\infty^{\mathrm{critical}}\right)^q\right].

This refines Harper's question about a nontrivial critical distributional limit. The supplied text presents it as a precise conjecture and gives no resolution, so the existence and properties of the critical limiting random measure remain open.

References

Primary source

Ofir Gorodetsky and Mo Dick Wong, “Martingale central limit theorem for random multiplicative functions”, arXiv:2405.20311 (2024).

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