Hörmander–Mikhlin conjecture for stratified Lie groups

From papers

Let G\mathrm{G} be an nn-dimensional stratified Lie group with homogeneous dilation weights (1,2,,n)(\ell_1,\ell_2,\ldots,\ell_n), rescaled so that min(j)=1\min(\ell_j)=1, and let LSR:GR+L_\mathrm{SR}:\mathrm{G}\to\mathbf{R}_+ be the associated subRiemannian length. For a multi-index γ\gamma, write {γ}=j=1njγj\{\gamma\}=\sum_{j=1}^n\ell_j\gamma_j, and let dgγd_g^\gamma denote the corresponding derivative of a Fourier symbol m:GCm:\mathrm{G}\to\mathbf{C}. HM for stratified Lie groups. For every 1<p<1<p<\infty, the Fourier multiplier TmT_m satisfies

Tm:Lp(L(G))Lp(L(G))cbp2p1γ[n2]+1LSR(g){γ}dgγm(g).\big\|T_m:L_p(\mathcal{L}(G))\to L_p(\mathcal{L}(G))\big\|_{\mathrm{cb}}\lesssim\frac{p^2}{p-1}\sum_{|\gamma|\leq\left[\frac n2\right]+1}\big\|L_\mathrm{SR}(g)^{\{\gamma\}}d_g^\gamma m(g)\big\|_\infty.

This is a proposed stratified analogue of the anisotropic Hörmander–Mikhlin theorem, extending the Euclidean and anisotropic multiplier criteria to Fourier multipliers on stratified Lie groups; the parser supplies no evidence resolving it.

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Primary source

José M. Conde-Alonso, Adrián M. González-Pérez, Javier Parcet and Eduardo Tablate, “A Hörmander-Mikhlin theorem for high rank simple Lie groups”, arXiv:2201.08740 (2024).

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