The Boundedness of the Bilinear Fractional Integrals along Curves

TL;DR

This paper establishes boundedness results for bilinear fractional integrals and fractional integral operators along curves with curvature conditions, extending classical inequalities in harmonic analysis.

Contribution

It provides new $L^p$ estimates for bilinear fractional integrals and sharp Hardy-Littlewood-Sobolev inequalities along curved trajectories.

Findings

Derived $L^p imes L^q o L^r$ estimates for bilinear integrals along curves.

Established almost sharp Hardy-Littlewood-Sobolev inequalities for fractional integrals along curves.

Extended classical harmonic analysis results to curved settings with curvature conditions.

Abstract

In this paper, for general curves $(t,\gamma(t))$ satisfying some suitable curvature conditions, we obtain some $L^p(\mathbb{R})\times L^q(\mathbb{R}) \rightarrow L^r(\mathbb{R})$ estimates for the bilinear fractional integrals $H_{\alpha,\gamma}$ along the curves $(t,\gamma(t))$, where $$H_{\alpha,\gamma}(f,g)(x):=\int_{0}^{\infty}f(x-t)g(x-\gamma(t))\,\frac{\textrm{d}t}{t^{1-\alpha}}$$ and $\alpha\in (0,1)$. At the same time, we also establish an almost sharp Hardy-Littlewood-Sobolev inequality, i.e., the $L^p(\mathbb{R})\rightarrow L^q(\mathbb{R})$ estimate, for the fractional integral operators $I_{\alpha,\gamma}$ along the curves $(t,\gamma(t))$, where $$I_{\alpha,\gamma}f(x):=\int_{0}^{\infty}\left|f(x-\gamma(t))\right|\,\frac{\textrm{d}t}{t^{1-\alpha}}.$$