Improved subconvexity bounds for GL(2)xGL(3) and GL(3) L-functions by weighted stationary phase

TL;DR

This paper establishes improved subconvexity bounds for certain automorphic L-functions related to GL(2) and GL(3), using advanced stationary phase techniques to refine previous results and achieve sharper bounds in different aspects.

Contribution

It introduces an $n$th-order asymptotic expansion of weighted stationary phase integrals, enhancing classical methods and leading to stronger subconvexity bounds for GL(2) and GL(3) L-functions.

Findings

Proved subconvexity bound $O(k^{4/3+ ext{ε}})$ for $L(1/2,f\times u)$ in eigenvalue aspect.

Established subconvexity bound $O((1+|t|)^{2/3+ ext{ε}})$ for $L(1/2+it,f)$ in the $t$-aspect.

Developed an $n$th-order asymptotic expansion method for weighted stationary phase integrals.

Abstract

Let $f$ be a fixed self-contragradient Hecke-Maass form for $SL(3,\mathbb Z)$, and $u$ an even Hecke-Maass form for $SL(2,\mathbb Z)$ with Laplace eigenvalue $1/4+k^2$, $k>0$. A subconvexity bound $O\big(k^{4/3+\varepsilon}\big)$ in the eigenvalue aspect is proved for the central value at $s=1/2$ of the Rankin-Selberg $L$-function $L(s,f\times u)$. Meanwhile, a subconvexity bound $O\big((1+|t|)^{2/3+\varepsilon}\big)$ in the $t$ aspect is proved for $L(1/2+it,f)$. These bounds improved corresponding subconvexity bounds proved by Xiaoqing Li (Annals of Mathematics, 2011). The main technique in the proof, other than those used by Li, is an $n$th-order asymptotic expansion of a weighted stationary phase integral, for arbitrary $n\geq1$. This asymptotic expansion sharpened the classical result for $n=1$ by Huxley.