Critical-limit conjecture for random multiplicative functions

From papers

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

Vcritical:=limx12πRloglogxmx,(ds)12+is2=12πRmcritical(ds)12+is2,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 mcritical(ds):=limxloglogxmx,(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 VcriticalV_\infty^{\mathrm{critical}} is almost surely finite and strictly positive, and, independently of GNC(0,1)G\sim\mathcal{N}_{\mathbb{C}}(0,1),

(loglogx)1/4xnxα(n)f(n)xdVcriticalG.\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),

limxE[(loglogx)1/4xnxα(n)f(n)2q]=Γ(1+q)E[(Vcritical)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.

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Sources & referencesView supporting material

Primary source

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

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