A weighted composition semigroup related to three open problems

Abstract: The semi-group of weighted composition operators $(W_n){n\geq 1}$ where [ W_nf(z)=(1+z+\ldots+z^{n-1})f(z^n) ] on the classical Hardy-Hilbert space $H^2$ of the open unit disk is related to the Riemann Hypothesis (RH) (see \cite{Waleed}). The semigroup $(W_n){n\geq 1}$ is also closely related to the Invariant Subspace Problem (ISP) and the Periodic Dilation Completeness Problem (PDCP). We obtain results on cyclic vectors, spectra, invariant and reducing subspaces. In particular, we show that several basic questions related to the semigroup $(W_n)_{n\geq 1}$ are equivalent to the RH and provide generalizations of the B\'aez-Duarte criterion for the RH (see \cite{Baez-Duarte}).