On the Calderon-Zygmund property of Riesz-transform type operators arising in nonlocal equations (2007.04173v1)

Abstract: We show that the operator [ T_{K,s_1,s_2}f(z) := \int_{\mathbb{R}^n} A_{K,s_1,s_2}(z_1,z_2) f(z_2)\, dz_2 ] is a Calderon-Zygmund operator. Here for $K \in L^\infty(\mathbb{R}^n \times \mathbb{R}^n)$, and $s,s_1,s_2 \in (0,1)$ with $s_1+s_2 = 2s$ we have [ A_{K,s_1,s_2}(z_1,z_2) = \int_{\mathbb{R}^n} \int_{\mathbb{R}^n} \frac{K(x,y) \left (|x-z_1|^{s_1-n} -|y-z_1|^{s_1-n} \right )\, \left (|x-z_2|^{s_2-n} -|y-z_2|^{s_2-n}\right )}{|x-y|^{n+2s}}\, dx\, dy. ] This operator is motivated by the recent work by Mengesha-Schikorra-Yeepo where it appeared as analogue of the Riesz transforms for the equation [ \int_{\mathbb{R}^n} \int_{\mathbb{R}^n} \frac{K(x,y) (u(x)-u(y))\, (\varphi(x)-\varphi(y))}{|x-y|^{n+2s}}\, dx\, dy = f[\varphi]. ]