Fourier Coefficients of Automorphic Forms

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865 Roelof W. Bruggeman

Fourier Coefficients of Automorphic Forms

Springer-Verlag Berlin Heidelberg New York 1981

Author

Roelof W. Bruggeman Mathematisch Instituut, Rijksuniversiteit Utrecht Budapestlaan 6, Utrecht, The Netherlands

AMS Subject Classifications (1980): 10D15, 10D40, 22 E40, 42A 16, 43A65, 44A 15 ISBN 3-540-10839-4 Springer-Verlag Berlin Heidelberg New York ISBN 0-387-10839-4 Springer-Verlag New York Heidelberg Berlin

This work is subject to copyright. All rights are reserved, whether the whole or part of the material is concerned, specifically those of translation, reprinting, re-use of illustrations, broadcasting, reproduction by photocopying machine or similar means, and storage in data banks. Under § 54 of the German Copyright Law where copies are made for other than private use, a fee is payable to "Verwertungsgesellschaft Wort", Munich.

© by Springer-Verlag Berlin Heidelberg 1981 Printed in Germany

Printing and binding: Beltz Offsetdruck, Hemsbach/Bergstr. 2141/3140-543210

Table of contents Introduction 2

The universal covering group G

19

3

Representations

24

4

Automorphic models

33

5

Standard and Whittaker models

41

6

Intertwining operators

49

7

Fourier coefficients of automorphic models

61

8

The operators G a Eisenstein models

72

9

84

2

10

L ( I'\ G, X)

11

The analytic continuation of the Eisenstein model

12

Spectral decomposition of

93 e 2

L (I'\G,X)

T

103 J 25

13

The space H

133

14

Convolution operators

148

15

Scalar product of Poincare series

166

16

Sum formula

177

Literature

196

o

Index of notations

198

Index of terminology

201

I. Introduction.

1.1. A sum formula for the modular case

To give an idea of the subject of these notes I discuss in this subsection a simple case. Holomorphic modular cusp forms are well known; of many possible references I mention [23], [39], [42]. These cusp forms are holomorphic functions on the upper half plane h ; {z E Cllm z

> a},

(1.1.1)

satisfying the transformation property

Ct,S,y,o Ell, CtO-Sy; I, yz+u for some positive even number b, the weight, and having a Fourier series expansion fez) ; a e2rrinz. (1.1.2) The numbers a

; (yz+o)bf(z),

n

are

n

the Fourier coefficients of f. For a fixed weight b the

space of such cusp forms has finite dimension; it may be provided with the Petersson scalar product. For fixed n the map f be described as f

(f,p)

n p

an is linear on such a space, hence it may

for some cusp form p . By (.,.) n

p

I denote the Petersson

scalar product. Up to a multiple this Pn is given by a Poincare series. Petersson has given a formula for the Fourier coefficients of these Poincare series, see [ 28] or [23], p.298. The n-th Fourier coefficient of the m-th Poincare series of weight b equals

Ib Ib- I 00 -I 1 ro + 2rr(-l) 2 (n/m) 2 2 L S(n,m;c)c J (4rrc- "mn). m,n b_ 1 J _ is a Bessel function, and is a Kloosterman sum: b 1 (1.1.4) S(n,m;c); L e2rric-l(nx+mx-; x mod c (x,c);1 with xX=' I(c). (1.1.3)

Let f

I'" .,f be an orthonormal basis for the space of cusp fo