(Uniform) Convergence of Twisted Ergodic Averages

Abstract

Let $T$ be an ergodic measure-preserving transformation on a non-atomic probability space $(X,\Sigma,\mu)$. We prove uniform extensions of the Wiener-Wintner theorem in two settings: For averages involving weights coming from Hardy field functions, $p$: \[ \{\frac{1}{N} \sum_{n\leq N} e(p(n)) T^{n}f(x) \} \] and for "twisted" polynomial ergodic averages: \[ \{\frac{1}{N} \sum_{n\leq N} e(n \theta) T^{P(n)}f(x) \} \] for certain classes of badly approximable $\theta \in [0,1]$. We also give an elementary proof that the above twisted polynomial averages converge pointwise $\mu$-a.e. for $f \in L^p(X), \ p >1,$ and arbitrary $\theta \in [0,1]$.