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Subconvexity bounds for Rankin-Selberg L-functions for congruence subgroups
Journal article   Open access   Peer reviewed

Subconvexity bounds for Rankin-Selberg L-functions for congruence subgroups

Yuk Kam Lau, Jianya Liu and Yangbo Ye
Journal of number theory, Vol.121(2), pp.204-223
2006
DOI: 10.1016/j.jnt.2006.02.006
url
https://doi.org/10.1016/j.jnt.2006.02.006View
Published (Version of record) Open Access

Abstract

Estimation of shifted sums of Fourier coefficients of cusp forms plays crucial roles in analytic number theory. Its known region of holomorphy and bounds, however, depend on bounds toward the general Ramanujan conjecture. In this article, we extended such a shifted sum meromorphically to a larger half plane Re s > 1 / 2 and proved a better bound. As an application, we then proved a subconvexity bound for Rankin–Selberg L -functions which does not rely on bounds toward the Ramanujan conjecture: Let f be either a holomorphic cusp form of weight k , or a Maass cusp form with Laplace eigenvalue 1 / 4 + k 2 , for Γ 0 ( N ) . Let g be a fixed holomorphic or Maass cusp form. What we obtained is the following bound for the L -function L ( s , f ⊗ g ) in the k aspect: L ( 1 / 2 + i t , f ⊗ g ) ≪ k 1 − 1 / ( 8 + 4 θ ) + ε , where θ is from bounds toward the generalized Ramanujan conjecture. Note that a trivial θ = 1 / 2 still yields a subconvexity bound.

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