Spectral Reciprocity and Hybrid Subconvexity Bound for triple product $L$-functions

Abstract

Let $F$ be a number field with adele ring $\mathbb{A}_F$, $\pi_1, \pi_2$ be two unitary cuspidal automorphic representations of $\mathrm{PGL}_2(\mathbb{A}_F)$ with finite analytic conductor. We study the twisted first moment of the triple product $L$-function $L(\frac{1}{2}, \pi \otimes \pi_1 \otimes \pi_2)$ and the Hecke eigenvalues $\lambda_\pi (\mathfrak{l})$, where $\pi$ is a unitary automorphic representation of $\mathrm{PGL}_2(\mathbb{A}_F)$ and $\mathfrak{l}$ is an integral ideal coprimes with the finite analytic conductor $C(\pi \otimes \pi_1 \otimes \pi_2)$. The estimation becomes a reciprocity formula between different moments of $L$-functions. Combining with the ideas and estimations established in [HMN23] and [MV10], we study the subconvexity problem for the triple product $L$-function in the level aspect and give a new explicit hybrid subconvexity bound for $L(\frac{1}{2}, \pi \otimes \pi_1 \otimes \pi_2)$, allowing joint ramifications and conductor dropping range.