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Upper bounds for geodesic periods over rank one locally symmetric spaces

  • Jan Frahm ORCID logo EMAIL logo and Feng Su ORCID logo
Published/Copyright: January 13, 2018

Abstract

We prove upper bounds for geodesic periods of automorphic forms over general rank one locally symmetric spaces. Such periods are integrals of automorphic forms restricted to special totally geodesic cycles of the ambient manifold and twisted with automorphic forms on the cycles. The upper bounds are in terms of the Laplace eigenvalues of the two automorphic forms, and they generalize previous results for real hyperbolic manifolds to the context of all rank one locally symmetric spaces.

MSC 2010: 11F70; 22E46; 53C35

Communicated by Jan Bruinier


A Integral formulas

For α,β>0 and 0<Reλ<2Re(μ+ν), we have (see [11, equation 3.259 (3)])

(A.1)0xλ-1(1+αx2)-μ(1+βx2)-ν𝑑x=12α-λ2B(λ2,μ+ν-λ2)F12(ν,λ2;μ+ν;1-βα).

The Euler transformation formula holds (see [1, (2.2.7)]):

(A.2)F12(α,β;γ;x)=(1-x)γ-α-βF12(γ-α,γ-β;γ;x).

The Euler integral representation holds for Re(γ-β),Reβ>0 (see [1, (2.3.17)]):

(A.3)F12(α,β;γ;1-x)=Γ(γ)Γ(γ-β)Γ(β)0tβ-1(1+t)α-γ(1+xt)-α𝑑t.

The following integral formula holds for 0β<1 and 0<Reμ<Re(λ-2ν) (see [11, equation 3.254 (2)] for λ=0 and u=1):

(A.4)1(x-1)μ-1(x2+β)ν𝑑x=Γ(μ)Γ(-μ-2ν)Γ(-2ν)F12(-μ2-ν,1-μ2-ν;12-ν;-β).

By using Pfaff’s transformation formula (see [1, (2.2.6)])

F12(α,β;γ;x)=(1-x)-αF12(α,γ-β;γ;xx-1)

and the integral formula

01xρ-1(1-x)σ-1F12(α,β;γ;x)𝑑x=Γ(ρ)Γ(σ)Γ(ρ+σ)F23(α,β,ρ;γ,ρ+σ;1)

which holds for Reρ,Reσ,Re(γ+σ-α-β)>0 (see [11, equation 7.512 (5)]), it is easy to see by a simple substitution that for Reρ,Re(α-σ-ρ+1),Re(β-σ-ρ+1)>0 we have

(A.5)0xρ-1(1+x)σ-1F12(α,β;γ;-x)𝑑x=Γ(ρ)Γ(α-σ-ρ+1)Γ(α-σ+1)F23(α,γ-β,ρ;γ,α-σ+1;1).

For Re(γ-α-β)>0, we have the Gauß special value (see [1, Theorem 2.2.2])

(A.6)F12(α,β;γ;1)=Γ(γ)Γ(γ-α-β)Γ(γ-α)Γ(γ-β).

For Reμ,Reν>0, we have (see [11, equation 3.621 (5)])

(A.7)0π2sinμ-1θcosν-1θdθ=12B(μ2,ν2).

Acknowledgements

The authors thank the referee for many helpful comments and remarks that helped to improve the exposition.

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Received: 2017-09-04
Revised: 2017-11-29
Published Online: 2018-01-13
Published in Print: 2018-09-01

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