Almost-everywhere convergence of Fourier series for functions in Sobolev spaces

Abstract

Let $S_{\lambda }F(x)$ be the spherical partial sums of the multiple Fourier series of function $F\in L_2({\mathbb{T}}^N)$. We prove almost-everywhere convergence $S_{\lambda }F(x)\to F(x)$ for functions in Sobolev spaces $H_p^a({\mathbb{T}}^N)$ provided $1<p\le 2$ and $a>(N-1)(\frac{1}{p}-\frac{1}{2})$. For multiple Fourier integrals this is well known result of Carbery and Soria (1988). To prove our result, we first extend the transplantation technic of Kenig and Tomas (1980) from $L_p$ spaces to $H_p^a$ spaces, then apply it to the Carbery and Soria result.

arXiv comment5 pages