Published online by Cambridge University Press: 08 March 2019
For a complex function $F$ on
$\mathbb{C}$, we study the associated composition operator
$T_{F}(f):=F\circ f=F(f)$ on Wiener amalgam
$W^{p,q}(\mathbb{R}^{d})\;(1\leqslant p<\infty ,1\leqslant q<2)$. We have shown
$T_{F}$ maps
$W^{p,1}(\mathbb{R}^{d})$ to
$W^{p,q}(\mathbb{R}^{d})$ if and only if
$F$ is real analytic on
$\mathbb{R}^{2}$ and
$F(0)=0$. Similar result is proved in the case of modulation spaces
$M^{p,q}(\mathbb{R}^{d})$. In particular, this gives an affirmative answer to the open question proposed in Bhimani and Ratnakumar (J. Funct. Anal. 270(2) (2016), 621–648).