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In this paper, we study the L2 functions on U (2 n) / O (2 n) and Mp (n, R). We relate them using the oscillator representation. We first study some isometries between various L2 spaces using the compactification we defined in [H. He, An analytic compactification of the symplectic group, J. Differential Geom. 51 (1999) 375-399]. These isometries were first introduced by Betten and Ólafsson in [F. Betten, G. Ólafsson, Causal compactification and Hardy spaces for spaces of Hermitian type, Pacific J. Math. 200 (2) (2001) 273-312].11I was informed by Prof. Ólafsson of his work shortly after I finished this paper. We then give a description of the matrix coefficients of the oscillator representation ω in terms of algebraic functions on U (2 n) / O (2 n). The structure of L2 (U (2 n) / O (2 n)) enables us to decompose the L2 space of odd functions on Mp (n, R) into a finite orthogonal direct sum, from which an orthogonal basis for L2 (Mp (n, R)) is obtained. In addition, our decomposition preserves both left and right Mp (n, R)-action. Using this, we define the signature of tempered genuine representations of Mp (n, R). Our result implies that every genuine discrete series representation occurs as a subrepresentation in one and only one of (⊗p ω) ⊗ (⊗2 n + 1 - p ω*) for p with a fixed parity, generalizing some result in [M. Kashiwara, M. Vergne, On the Segal-Shale-Weil representations and harmonic polynomials, Invent. Math. 44 (1978) 1-47]. Consequently, we prove some results in the papers by Adams and Barbasch [J. Adams, D. Barbasch, Genuine representations of the metaplectic group, Compos. Math. 113 (1) (1998) 23-66] and by Móeglin [C. Móeglin, Correspondance de Howe pour les paires reductives duales: quelques calculs dans le cas archimédien, J. Funct. Anal. 85 (1) (1989) 1-85] without going through the details of the Langlands-Vogan parameter. In a weak sense, our paper also provides an analytic alternative to the Adams-Barbasch theorem on Howe duality [R. Howe, Transcending invariant theory, J. Amer. Math. Soc. 2 (1989) 535-552]. © 2006 Elsevier Inc. All rights reserved.

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Journal of Functional Analysis

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