On the Effective Non-vanishing of Rankin--Selberg $L$-functions at Special Points

Abstract: Let $Q (z)$ be a holomorphic Hecke cusp newform of square-free level and $u_j (z)$ traverse an orthonormal basis of Hecke--Maass cusp forms of full level. Let $1/4 + t_j^2$ be the Laplace eigenvalue $u_j (z)$. In this paper, we prove that there is a constant $ \gamma (Q) $ expressed as a certain Euler product associated to $Q$ such that at least $ \gamma (Q) / 11 $ of the Rankin--Selberg special $L$-values $L (1/2+it_j, Q \otimes u_j)$ for $ t_j \leqslant T$ do not vanish as $T \rightarrow \infty$. Further, we show that the non-vanishing proportion is at least $\gamma (Q) \cdot (4\mu-3) / (4\mu+7) $ on the short interval $ |t_j - T| \leqslant T^{\mu} $ for any $3/4 < \mu < 1$.