Shifted Convolution Sums for $GL(3)\times GL(2)$ Averaged over weighted sets

Wing Hong Leung

Published 2022-10-24Version 1

Let $A(1,m)$ be the Fourier coefficients of a $SL(3,\mathbb{Z})$ Hecke-Maass cusp form $\pi_1$ and $\lambda(m)$ be those of a $SL(2,\mathbb{Z})$ Hecke holomorphic or Hecke-Mass cusp form $\pi_2$. Let $\mathcal{H}\subset[\![ -X^{1-\varepsilon},X^{1+\varepsilon}]\!]$ and $\{a(h)\}_{h\in\mathcal{H}}\subset\mathbb{C}$ be a sequence. We show that if $\mathcal{H}\subset \ell+[\![ 0,X^{1/2+\varepsilon}]\!] $ for some $\ell\geq0$, \begin{align*} D_{a,\mathcal{H}}(X):=\frac{1}{|\mathcal{H}|}\sum_{h\in\mathcal{H}}a(h)\sum_{m=1}^\infty A(1,m)\lambda(rm+h)V\left(\frac{m}{X}\right)\ll_{\pi_1,\pi_2,\varepsilon} \frac{X^{1+\varepsilon}}{|\mathcal{H}|}\|a\|_2 \end{align*} for any $\varepsilon>0$, and a similar bound when $|\mathcal{H}|$ is big. This improves Sun's bound and generalizes it to an average with arbitrary weights. Moreover, we demonstrate how one can recover the factorizable moduli structure given by the Jutila's circle method via studying a shifted sum with weighted average. This allows us to recover Munshi's bound on the shifted sum with a fixed shift without using the Jutila's circle method.