Threshold conjecture for positivity of partial sums of a random multiplicative function

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Let ff be a random completely multiplicative function taking values in 1,−1\\{1,-1\\}, with the values f(p)f(p) chosen independently and uniformly at random over the primes. Let Lx+\mathcal{L}_x^+ be the set of such functions for which ∑n≤tf(n)≥0\sum_{n\leq t}f(n)\geq 0 for every integer 1≤t≤x1\leq t\leq x. For y≥1y\geq 1, condition on f(p)=1f(p)=1 for every prime p≤yp\leq y. Threshold conjecture. For every ε>0\varepsilon>0, there is x0(ε)x_0(\varepsilon) such that, whenever x>x0(ε)x>x_0(\varepsilon) and y≤(log⁡x)2−εy\leq(\log x)^{2-\varepsilon},

P⁡(f∈Lx+∣f(p)=1(p≤y))=o(1).\operatorname{\mathbb{P}}\left(f\in\mathcal{L}_x^+\mid f(p)=1\\ (p\leq y)\right)=o(1).

Together with the proved upper-threshold result at y≫(log⁡x)2log⁡2x/log⁡3xy\gg (\log x)^2\log_2x/\log_3x, this would locate the transition for conditioned positivity near y=(log⁡x)2+o(1)y=(\log x)^{2+o(1)}.

References

Primary source

Petr Kucheriaviy, “Positivity of partial sums of a random multiplicative function and corresponding problems for the Legendre symbol”, arXiv:2510.25691 (2026).

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