Oscillation results for the summatory functions of fake mu's

Abstract: Mossinghoff, Trudgian, and the first author~\cite{MMT23} recently introduced a family of arithmetic functions called fake $\mu$'s'', which are multiplicative functions for which there is a $\{-1,0,1\}$-valued sequence $(\varepsilon_j)_{j=1}^{\infty}$ such that $f(p^j) = \varepsilon_j$ for all primes $p$. They investigated comparative number-theoretic results for fake $\mu$'s and in particular proved oscillation results at scale $\sqrt{x}$ for the summatory functions of fake $\mu$'s with $\varepsilon_1=-1$ and $\varepsilon_2=1$. In this paper, we establish new oscillation results for the summatory functions of all nontrivial fake $\mu$'s at scales $x^{1/2\ell}$ where $\ell$ is a positive integer (thecritical index'') depending on $f$; for $\ell=1$ this recovers the oscillation results in~\cite{MMT23}. Our work also recovers results on the indicator functions of powerfree and powerfull numbers; we generalize techniques applied to each of these examples to extend to all fake $\mu$'s.