On the second integral moment of $L$-functions

Abstract

Assume that the generalized Ramanujan conjecture holds on the automorphic $L$-function $L(s, π)$ on $\GL_d$ over $\mathbb{Q}$ with $d\geq 3$, we can obtain a small log-saving non-trivial bound on the second integral moment of $L(1/2+it, π)$. Specifically the bound \[ \int_{T}^{2T}\Big|L\big(\frac{1}{2}+it, π\big)\Big |^2 \dd t\ll_π \frac{T^{\frac{d}{2}}}{\log^{η_d}T} \] holds for a small constant $η_d>0$.