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Aug 17, 2021 at 11:13 comment added Benjamin Thank you for the comment and for taking time to think about the problem, although it is of course not the answer I hoped for. ;)
Aug 17, 2021 at 7:32 comment added Giorgio Metafune I do not think you can go far beyond a linear growth. Let $\hat g=\eta$ so that $g$ is in the Schwartz class and $\eta(-i\nabla) h=g*h$. Then the commutator is given by $$Ch(x)=\int_{\bf R^n}g(y) (f(x-y)-f(x))h(x-y)\, dy.$$ If $|f(x-y)-f(x)| \leq A(y)$ and $gA$ is in $L^1$, then $C$ is bounded by Young's inequality for convolutions. However this imples a linear growth for $f$, since the estimate is independent of $x$. If $f(x)=x^2$ (1d), the above difference is $2xy+y^2$. The $y^2$ term is treated as above, but the extra $x$ can make $C$ unbounded. I did not work the details, however.
Aug 17, 2021 at 6:16 history edited Benjamin CC BY-SA 4.0
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Aug 16, 2021 at 17:44 history asked Benjamin CC BY-SA 4.0