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A new bound K2/3+
for Rankin-Selberg
-functions for Hecke congruence subgroups
Department of Mathematics, The University of Hong Kong Pokfulam Road, Hong Kong E-mail address: yklau{at}maths.hku.hk
Department of Mathematics, Shandong University 227 Shanda Nanlu, Jinan, Shandong 250100, China E-mail address: jyliu{at}sdu.edu.cn
Department of Mathematics, The University of Iowa 14 MacLean Hall, Iowa City, IA 52242-1419, USA E-mail address: yey{at}math.uiowa.edu
Let f be a holomorphic Hecke eigenform for
0(N) of weight k, or a Maass eigenform for
0(N) with Laplace eigenvalue 1/4 + k2. Let g be a fixed holomorphic or Maass cusp form for
0(N). A subconvexity bound for central values of the Rankin-Selberg L-function L(s, f
g) is proved in the k-aspect: L(1/2 + it, f
g) <<N,g,t,
k2/3+
, while a convexity bound is only << k1+
. The dependence of the implied constant on t and the level N is polynomial. This new bound improves earlier subconvexity bounds for these Rankin-Selberg L-functions by Sarnak, the authors, and Blomer. Techniques used include a result of Good, spectral large sieve, meromorphic continuation of a shifted convolution sum to
e s > 1/2 passing through all Laplace eigenvalues, and a weighted stationary phase argument.