Suppose
$2< p<\infty$
and
$\varphi$
is a holomorphic self-map of the open unit disk
$\mathbb {D}$
. We show the following assertions:
(1)
If
$\varphi$
has bounded valence and
0.1
\begin{equation} \int_{\mathbb{D}} \left(\frac{1-|z|^2}{1-|\varphi(z)|^2}\right)^{p/2}\frac{\mathrm{d} A(z)}{(1-|z|^2)^2}<\infty, \end{equation}
then
$C_{\varphi }$
is in the Schatten
$p$
-class of the Hardy space
$H^2$
.
(2)
There exists a holomorphic self-map
$\varphi$
(which is, of course, not of bounded valence) such that the inequality (0.1) holds and
$C_{\varphi }: H^2\to H^2$
does not belong to the Schatten
$p$
-class.