Bounds for discrete multilinear spherical maximal functions (1910.11409v2)

Abstract: We define a discrete version of the bilinear spherical maximal function, and show bilinear $l^{p}(\mathbb{Z}^d)\times l^{q}(\mathbb{Z}^d) \to l^{r}(\mathbb{Z}^d)$ bounds for $d \geq 3$, $\frac{1}{p} + \frac{1}{q} \geq \frac{1}{r}$, $r>\frac{d}{d-2}$ and $p,q\geq 1$. Due to interpolation, the key estimate is an $l^{p}(\mathbb{Z}^d)\times l^{\infty}(\mathbb{Z}^d) \to l^{p}(\mathbb{Z}^d)$ bound, which holds when $d \geq 3$, $p>\frac{d}{d-2}$. A key feature of our argument is the use of the circle method which allows us to decouple the dimension from the number of functions compared to the work of Cook.