Seek a reference for Theorem 1.2 on p. 6 of the Riemann Hypothesis sourcebook of Borwein et. al

Question

The book "The Riemann Hypothesis, A Resource for the Afficionado and Virtuoso Alike", Borwein, Choi, Rooney, Weirathmueller, Eds., states on its page six the following theorem (Theorem 1.2):

The Riemann hypothesis is equivalent to the statement that for every fixed $\epsilon > 0$,

$$\lim_{n \to \infty} \frac{\lambda(1) + \lambda(2)+ ...+\lambda(n)}{n^{\frac 12 + \epsilon}} = 0.$$

(Here, $\lambda$ is the Liouville function $\lambda: n \mapsto (-1)^{\omega(n)}$ where $\omega(n)$ is the number of, not necessarily distinct, prime factors of $n$.) The editors remark that this statement among others were considered by Landau in his doctoral thesis of 1899. There is translation by Coons of a dissertation of Landau, which is described as his doctoral dissertation, here:

https://arxiv.org/abs/0803.3787

But I haven't been able to discern a direct connection between this article and the theorem above. Am I missing something? Is there perhaps a proof of this theorem available somewhere else? I've looked a bit, and I haven't found one.

Reason for asking: I wonder, under the Riemann hypothesis, what happens to the exponent in the denominator if powers of $-1$ in the definition of the Liouville function are replaced by powers of some other root of unity $\exp(2 \pi i/k), k >2$.

Answer 1

About your reason for asking. See https://doi.org/10.1215/00277630-1260423, https://projecteuclid.org/euclid.nmj/1306851587 or the arxiv version https://arxiv.org/pdf/0906.1029.pdf where such things are discussed. In particular, the partial sums $\sum_{n\leq x}\exp(2\pi i\Omega(n)/k)$ are not $o(x^\alpha)$ for any $\alpha<1$.