Sharp $\ell^p$ inequalities for discrete singular integrals
arxiv(2022)
1$ is motivated by a similar problem, Conjecture 5.5, concerning the norm of the discrete Riesz transforms arising from discretizing singular integrals on $\mathbb{R}^d$ as in the original paper of A. P. Calder\'on and A. Zygmund, and subsequent works of A. Magyar, E. M. Stein, S. Wainger, L. B. Pierce and many others, concerning operator norms in discrete harmonic analysis. For any $d\geq 1$, it is shown that the probabilistic discrete Riesz transforms have the same $\ell^p$ norm as the continuous Riesz transforms on $\mathbb{R}^d$ which is dimension independent and equals the norm of the classical Hilbert transform on $\mathbb{R}$. Along the way we give a different proof, based on Fourier transform techniques, of the key estimate used to identify the norm of the discrete Hilbert transform.