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

From papers

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 ntf(n)0\sum_{n\leq t}f(n)\geq 0 for every integer 1tx1\leq t\leq x. For y1y\geq 1, condition on f(p)=1f(p)=1 for every prime pyp\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(logx)2εy\leq(\log x)^{2-\varepsilon},

P(fLx+f(p)=1(py))=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(logx)2log2x/log3xy\gg (\log x)^2\log_2x/\log_3x, this would locate the transition for conditioned positivity near y=(logx)2+o(1)y=(\log x)^{2+o(1)}.

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Sources & referencesView supporting material

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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