Uniform bounds for the bilinear Hilbert transforms, I


It is shown that the bilinear Hilbert transforms \[ H_{\alpha,\beta} (f,g)(x) = \text{p.v.}\int_{\mathbf{R}} f(x-\alpha t)g(x-\beta t)\, \frac{dt}{t} \] map $L^{p_1}(\mathbf{R})\times L^{p_2}(\mathbf{R})\to L^p(\mathbf{R})$ uniformly in the real parameters $\alpha,\beta $ when $2 < p_1, p_2 < \infty$ and $1\lt p= \frac{p_1p_2}{p_1+p_2}<2$. Combining this result with the main result in [9], we deduce that the operators $H_{1, \alpha}$ map $L^2(\mathbf{R})\times L^\infty(\mathbf{R})\to L^2(\mathbf{R})$ uniformly in the real parameter $\alpha\in [0,1]$. This completes a program initiated by A. Calderón.


Loukas Grafakos

Department of Mathematics, University of Missouri, Columbia, MO 65211, United States

Xiaochun Li

Department of Mathematics, University of California, Los Angeles, Los Angeles, CA 90095, United States