Strong Hybrid Subconvexity for Twisted Selfdual GL₃ L-Functions

We prove strong hybrid subconvex bounds simultaneously in the q and t aspects for L-functions of selfdual GL₃ cusp forms twisted by primitive Dirichlet characters. We additionally prove analogous hybrid subconvex bounds for central values of certain GL₃ × GL₂ Rankin-Selberg L-functions. The subconvex bounds that we obtain are strong in the sense that, modulo current knowledge on estimates for the second moment of GL₃ L-functions, they are the natural limit of the first moment method pioneered by Li and by Blomer. The method of proof relies on an explicit GL₃ × GL₂ GL₄ × GL₁ spectral reciprocity formula, which relates a GL₂ moment of GL₃ × GL₂ Rankin-Selberg L-functions to a GL₁ moment of GL₄ × GL₁ Rankin-Selberg L-functions. A key additional input is a Lindel\"of-on-average upper bound for the second moment of Dirichlet L-functions restricted to a coset, which is of independent interest.