English

Almost sure bounds for weighted sums of Rademacher random multiplicative functions

Number Theory 2026-02-04 v4 Probability

Abstract

We prove that when ff is a Rademacher random multiplicative function for any ϵ>0\epsilon>0, then nxf(n)n(loglog(x))3/4+ϵ\sum_{n \leqslant x}\frac{f(n)}{\sqrt{n}} \ll (\log\log(x))^{3/4+\epsilon} for almost all ff. We also show that there exist arbitrarily large values of xx such that nxf(n)n(loglog(x))1/2\sum_{n \leqslant x}\frac{f(n)}{\sqrt{n}} \gg (\log\log(x))^{-1/2}. This is different to what is found in the Steinhaus case, this time with the size of the Rademacher Euler product making the multiplicative chaos contribution the dominant one. We also find a sharper upper bound when we restrict to integers with a prime factor greater than x\sqrt{x}, proving that nxP(n)>xf(n)n(loglog(x))1/4+ϵ\sum_{\substack{n \leqslant x \\ P(n) > \sqrt{x}}}\frac{f(n)}{\sqrt{n}} \ll (\log\log(x))^{1/4+\epsilon}.

Keywords

Cite

@article{arxiv.2501.11076,
  title  = {Almost sure bounds for weighted sums of Rademacher random multiplicative functions},
  author = {Christopher Atherfold},
  journal= {arXiv preprint arXiv:2501.11076},
  year   = {2026}
}

Comments

50 pages. Comments welcome. Rewritten section 6.3 to attain a sharper bound, added references and improved introduction