Sub-convexity bound for $GL(3) \times GL(2)$ $L$-functions: $GL(3)$-spectral aspect

Sumit Kumar, Kummari Mallesham, Saurabh Kumar Singh

Published 2020-06-14Version 1

Let $\phi$ be a Hecke-Maass cusp form for $SL(3, \mathbb{Z})$ with Langlands parameters $({\bf t}_{i})_{i=1}^{3}$ satisfying $$|{\bf t}_{3} - {\bf t}_{2}| \leq T^{1-\xi -\epsilon}, \quad \, {\bf t}_{i} \approx T, \quad \, \, i=1,2,3$$ with $1/2 < \xi <1$ and any $\epsilon>0$. Let $f$ be a holomorphic or Maass Hecke eigenform for $SL(2,\mathbb{Z})$. In this article, we prove a sub-convexity bound $$L(\phi \times f, \frac{1}{2}) \ll \max \{ T^{\frac{3}{2}-\frac{\xi}{4}+\epsilon} , T^{\frac{3}{2}-\frac{1-2 \xi}{4}+\epsilon} \} $$ for the central values $L(\phi \times f, \frac{1}{2})$ of the Rankin-Selberg $L$-function of $\phi$ and $f$, where the implied constants may depend on $f$ and $\epsilon$. Conditionally, we also obtain a subconvexity bound for $L(\phi \times f, \frac{1}{2})$ when the spectral parameters of $\phi$ are in generic position, that is $${\bf t}_{i} - {\bf t}_{j} \approx T, \quad \, \text{for} \, i \neq j, \quad \, {\bf t}_{i} \approx T , \, \, i=1,2,3.$$