Multilinear transference of Fourier and Schur multipliers acting on non-commutative $L_p$-spaces

TL;DR

This paper extends transference principles from linear to multilinear Fourier and Schur multipliers on non-commutative $L_p$-spaces, establishing bounds and non-boundedness results for certain multilinear operators.

Contribution

It generalizes known transference results to the multilinear setting and analyzes boundedness properties of multilinear operators on non-commutative $L_p$-spaces.

Findings

Boundedness of multilinear Schur multipliers by Fourier multipliers in amenable groups.

Bilinear Hilbert transform is unbounded in certain vector-valued $L_p$-spaces.

Similar unboundedness results for Calderón-Zygmund operators.

Abstract

Let $G$ be a locally compact unimodular group, and let $\phi$ be some function of $n$ variables on $G$. To such a $\phi$, one can associate a multilinear Fourier multiplier, which acts on some $n$-fold product of the non-commutative $L_p$-spaces of the group von Neumann algebra. One may also define an associated Schur multiplier, which acts on an $n$-fold product of Schatten classes $S_p(L_2(G))$. We generalize well-known transference results from the linear case to the multilinear case. In particular, we show that the so-called `multiplicatively bounded $(p_1,\ldots,p_n)$-norm' of a multilinear Schur multiplier is bounded above by the corresponding multiplicatively bounded norm of the Fourier multiplier, with equality whenever the group is amenable. Further, we prove that the bilinear Hilbert transform is not bounded as a vector valued map $L_{p_1}(\mathbb{R}, S_{p_1}) \times L_{p_2}(\mathbb{R}, S_{p_2}) \rightarrow L_{1}(\mathbb{R}, S_{1})$, whenever $p_1$ and $p_2$ are such that $\frac{1}{p_1} + \frac{1}{p_2} = 1$. A similar result holds for certain Calder\'on-Zygmund type operators. This is in contrast to the non-vector valued Euclidean case.