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51. CJM 2009 (vol 61 pp. 1407)

Will, Pierre
 Traces, Cross-Ratios and 2-Generator Subgroups of $\SU(2,1)$ In this work, we investigate how to decompose a pair $(A,B)$ of loxodromic isometries of the complex hyperbolic plane $\mathbf H^{2}_{\mathbb C}$ under the form $A=I_1I_2$ and $B=I_3I_2$, where the $I_k$'s are involutions. The main result is a decomposability criterion, which is expressed in terms of traces of elements of the group $\langle A,B\rangle$. Categories:14L24, 22E40, 32M15, 51M10

52. CJM 2009 (vol 61 pp. 1325)

Nien, Chufeng
 Uniqueness of Shalika Models Let $\BF_q$ be a finite field of $q$ elements, $\CF$ a $p$-adic field, and $D$ a quaternion division algebra over $\CF$. This paper proves uniqueness of Shalika models for $\GL_{2n}(\BF_q)$ and $\GL_{2n}(D)$, and re-obtains uniqueness of Shalika models for $\GL_{2n}(\CF)$ for any $n\in \BN$. Keywords:Shalika models, linear models, uniqueness, multiplicity freeCategory:22E50

53. CJM 2009 (vol 61 pp. 961)

Bernon, Florent
 Transfert des intÃ©grales orbitales pour les algÃ¨bres de Lie classiques Dans cet article, on consid\ere un groupe semi-simple $\rmG$ classique r\'eel et connexe. On suppose de plus que $\rmG$ poss\ede un sous-groupe de Cartan compact. On d\'efinit une famille de sous-alg\ebres de Lie associ\'ee \a $\g = \Lie(\rmG)$, de m\^eme rang que $\g$ dont tous les facteurs simples sont de rang $1$ ou~$2$. Soit $\g'$ une telle sous-alg\ebre de Lie. On construit alors une application de transfert des int\'egrales orbitales de $\g'$ dans l'espace des int\'egrales orbitales de $\g$. On montre que cette application est d\'efinie d\es que $\g$ ne poss\ede pas de facteur simple r\'eel de type $\CI$ de rang sup\'erieur ou \'egal \a $3$. Si de plus, $\g$ ne poss\ede pas de facteur simple de type $\BI$ de rang sup\'erieur \a $3$, on montre la surjectivit\'e de cette application de transfert. On utilise cette application de transfert pour obtenir une formule de r\'eduction de l'int\'egrale de Cauchy Harish-Chandra pour les paires duales d'alg\ebres de Lie r\'eductives $\bigl( \Ug(p,q),\Ug(r,s) \bigr)$ et $\bigl( \Sp(p,q),\Og^*(2n) \bigr)$ avec $p+q = r+s = n$. Categories:22E30, 22E46

54. CJM 2009 (vol 61 pp. 779)

Grbac, Neven
 Residual Spectra of Split Classical Groups and their Inner Forms This paper is concerned with the residual spectrum of the hermitian quaternionic classical groups $G_n'$ and $H_n'$ defined as algebraic groups for a quaternion algebra over an algebraic number field. Groups $G_n'$ and $H_n'$ are not quasi-split. They are inner forms of the split groups $\SO_{4n}$ and $\Sp_{4n}$. Hence, the parts of the residual spectrum of $G_n'$ and $H_n'$ obtained in this paper are compared to the corresponding parts for the split groups $\SO_{4n}$ and $\Sp_{4n}$. Categories:11F70, 22E55

55. CJM 2009 (vol 61 pp. 708)

Zelenyuk, Yevhen
 Regular Homeomorphisms of Finite Order on Countable Spaces We present a structure theorem for a broad class of homeomorphisms of finite order on countable zero dimensional spaces. As applications we show the following. \begin{compactenum}[\rm(a)] \item Every countable nondiscrete topological group not containing an open Boolean subgroup can be partitioned into infinitely many dense subsets. \item If $G$ is a countably infinite Abelian group with finitely many elements of order $2$ and $\beta G$ is the Stone--\v Cech compactification of $G$ as a discrete semigroup, then for every idempotent $p\in\beta G\setminus\{0\}$, the subset $\{p,-p\}\subset\beta G$ generates algebraically the free product of one-element semigroups $\{p\}$ and~$\{-p\}$. \end{compactenum} Keywords:Homeomorphism, homogeneous space, topological group, resolvability, Stone-\v Cech compactificationCategories:22A30, 54H11, 20M15, 54A05

56. CJM 2009 (vol 61 pp. 691)

Yu, Xiaoxiang
 Prehomogeneity on Quasi-Split Classical Groups and Poles of Intertwining Operators Suppose that $P=MN$ is a maximal parabolic subgroup of a quasisplit, connected, reductive classical group $G$ defined over a non-Archimedean field and $A$ is the standard intertwining operator attached to a tempered representation of $G$ induced from $M$. In this paper we determine all the cases in which $\Lie(N)$ is prehomogeneous under $\Ad(m)$ when $N$ is non-abelian, and give necessary and sufficient conditions for $A$ to have a pole at $0$. Categories:22E50, 20G05

57. CJM 2009 (vol 61 pp. 373)

McKee, Mark
 An Infinite Order Whittaker Function In this paper we construct a flat smooth section of an induced space $I(s,\eta)$ of $SL_2(\mathbb{R})$ so that the attached Whittaker function is not of finite order. An asymptotic method of classical analysis is used. Categories:11F70, 22E45, 41A60, 11M99, 30D15, 33C15

58. CJM 2009 (vol 61 pp. 427)

 On Reducibility and Unitarizability for Classical $p$-Adic Groups, Some General Results The aim of this paper is to prove two general results on parabolic induction of classical $p$-adic groups (actually, one of them holds also in the archimedean case), and to obtain from them some consequences about irreducible unitarizable representations. One of these consequences is a reduction of the unitarizability problem for these groups. This reduction is similar to the reduction of the unitarizability problem to the case of real infinitesimal character for real reductive groups. Categories:22E50, 22E35

59. CJM 2009 (vol 61 pp. 351)

Graham, William; Hunziker, Markus
 Multiplication of Polynomials on Hermitian Symmetric spaces and Littlewood--Richardson Coefficients Let $K$ be a complex reductive algebraic group and $V$ a representation of $K$. Let $S$ denote the ring of polynomials on $V$. Assume that the action of $K$ on $S$ is multiplicity-free. If $\lambda$ denotes the isomorphism class of an irreducible representation of $K$, let $\rho_\lambda\from K \rightarrow GL(V_{\lambda})$ denote the corresponding irreducible representation and $S_\lambda$ the $\lambda$-isotypic component of $S$. Write $S_\lambda \cdot S_\mu$ for the subspace of $S$ spanned by products of $S_\lambda$ and $S_\mu$. If $V_\nu$ occurs as an irreducible constituent of $V_\lambda\otimes V_\mu$, is it true that $S_\nu\subseteq S_\lambda\cdot S_\mu$? In this paper, the authors investigate this question for representations arising in the context of Hermitian symmetric pairs. It is shown that the answer is yes in some cases and, using an earlier result of Ruitenburg, that in the remaining classical cases, the answer is yes provided that a conjecture of Stanley on the multiplication of Jack polynomials is true. It is also shown how the conjecture connects multiplication in the ring $S$ to the usual Littlewood--Richardson rule. Keywords:Hermitian symmetric spaces, multiplicity free actions, Littlewood--Richardson coefficients, Jack polynomialsCategories:14L30, 22E46

60. CJM 2009 (vol 61 pp. 222)

Nien, Chufeng
 Klyachko Models for General Linear Groups of Rank 5 over a $p$-Adic Field This paper shows the existence and uniqueness of Klyachko models for irreducible unitary representations of $\GL_5(\CF)$, where $\CF$ is a $p$-adic field. It is an extension of the work of Heumos and Rallis on $\GL_4(\CF)$. Keywords:Klyachko models, Whittaker-symplectic modelCategory:22E50

61. CJM 2008 (vol 60 pp. 1306)

Mui\'c, Goran
 Theta Lifts of Tempered Representations for Dual Pairs $(\Sp_{2n}, O(V))$ This paper is the continuation of our previous work on the explicit determination of the structure of theta lifts for dual pairs $(\Sp_{2n}, O(V))$ over a non-archimedean field $F$ of characteristic different than $2$, where $n$ is the split rank of $\Sp_{2n}$ and the dimension of the space $V$ (over $F$) is even. We determine the structure of theta lifts of tempered representations in terms of theta lifts of representations in discrete series. Categories:22E35, 22E50, 11F70

62. CJM 2008 (vol 60 pp. 1001)

Cornulier, Yves de; Tessera, Romain; Valette, Alain
 Isometric Group Actions on Hilbert Spaces: Structure of Orbits Our main result is that a finitely generated nilpotent group has no isometric action on an infinite-dimensional Hilbert space with dense orbits. In contrast, we construct such an action with a finitely generated metabelian group. Keywords:affine actions, Hilbert spaces, minimal actions, nilpotent groupsCategories:22D10, 43A35, 20F69

63. CJM 2008 (vol 60 pp. 1067)

Kariyama, Kazutoshi
 On Types for Unramified $p$-Adic Unitary Groups Let $F$ be a non-archimedean local field of residue characteristic neither 2 nor 3 equipped with a galois involution with fixed field $F_0$, and let $G$ be a symplectic group over $F$ or an unramified unitary group over $F_0$. Following the methods of Bushnell--Kutzko for $\GL(N,F)$, we define an analogue of a simple type attached to a certain skew simple stratum, and realize a type in $G$. In particular, we obtain an irreducible supercuspidal representation of $G$ like $\GL(N,F)$. Keywords:$p$-adic unitary group, type, supercuspidal representation, Hecke algebraCategories:22E50, 22D99

64. CJM 2008 (vol 60 pp. 790)

Blasco, Laure
 Types, paquets et changement de base : l'exemple de $U(2,1)(F_0)$. I. Types simples maximaux et paquets singletons Soit $F_0$ un corps local non archim\'edien de caract\'eristique nulle et de ca\-rac\-t\'eristique r\'esiduelle impaire. J. Rogawski a montr\'e l'existence du changement de base entre le groupe unitaire en trois variables $U(2,1)(F_{0})$, d\'efini relativement \a une extension quadratique $F$ de $F_{0}$, et le groupe lin\'eaire $GL(3,F)$. Par ailleurs, nous avons d\'ecrit les repr\'esentations supercuspidales irr\'eductibles de $U(2,1)(F_{0})$ comme induites \a partir d'un sous-groupe compact ouvert de $U(2,1)(F_{0})$, description analogue \a celle des repr\'esentations admissibles irr\'eductibles de $GL(3,F)$ obtenue par C. Bushnell et P. Kutzko. A partir de ces descriptions, nous construisons explicitement le changement de base des repr\'esentations tr\es cuspidales de $U(2,1)(F_{0})$. Categories:22E50, 11F70

65. CJM 2008 (vol 60 pp. 412)

Nguyen-Chu, G.-V.
 Quelques calculs de traces compactes et leurs transform{Ã©es de Satake On calcule les restrictions {\a} l'alg{\e}bre de Hecke sph{\'e}rique des traces tordues compactes d'un ensemble de repr{\'e}sentations explicitement construites du groupe $\GL(N, F)$, o{\u} $F$ est un corps $p$-adique. Ces calculs r\'esolve en particulier une question pos{\'e}e dans un article pr\'ec\'edent du m\^eme auteur. Categories:22E50, 11F70

66. CJM 2007 (vol 59 pp. 1301)

Furioli, Giulia; Melzi, Camillo; Veneruso, Alessandro
 Strichartz Inequalities for the Wave Equation with the Full Laplacian on the Heisenberg Group We prove dispersive and Strichartz inequalities for the solution of the wave equation related to the full Laplacian on the Heisenberg group, by means of Besov spaces defined by a Littlewood--Paley decomposition related to the spectral resolution of the full Laplacian. This requires a careful analysis due also to the non-homogeneous nature of the full Laplacian. This result has to be compared to a previous one by Bahouri, G\'erard and Xu concerning the solution of the wave equation related to the Kohn Laplacian. Keywords:nilpotent and solvable Lie groups, smoothness and regularity of solutions of PDEsCategories:22E25, 35B65

67. CJM 2007 (vol 59 pp. 1050)

Raghuram, A.
 On the Restriction to $\D^* \times \D^*$ of Representations of $p$-Adic $\GL_2(\D)$ Let $\mathcal{D}$ be a division algebra over a nonarchimedean local field. Given an irreducible representation $\pi$ of $\GL_2(\mathcal{D})$, we describe its restriction to the diagonal subgroup $\mathcal{D}^* \times \mathcal{D}^*$. The description is in terms of the structure of the twisted Jacquet module of the representation $\pi$. The proof involves Kirillov theory that we have developed earlier in joint work with Dipendra Prasad. The main result on restriction also shows that $\pi$ is $\mathcal{D}^* \times \mathcal{D}^*$-distinguished if and only if $\pi$ admits a Shalika model. We further prove that if $\mathcal{D}$ is a quaternion division algebra then the twisted Jacquet module is multiplicity-free by proving an appropriate theorem on invariant distributions; this then proves a multiplicity-one theorem on the restriction to $\mathcal{D}^* \times \mathcal{D}^*$ in the quaternionic case. Categories:22E50, 22E35, 11S37

68. CJM 2007 (vol 59 pp. 917)

 Admissibility for a Class of Quasiregular Representations Given a semidirect product $G = N \rtimes H$ where $N$ is%% nilpotent, connected, simply connected and normal in $G$ and where $H$ is a vector group for which $\ad(\h)$ is completely reducible and $\mathbf R$-split, let $\tau$ denote the quasiregular representation of $G$ in $L^2(N)$. An element $\psi \in L^2(N)$ is said to be admissible if the wavelet transform $f \mapsto \langle f, \tau(\cdot)\psi\rangle$ defines an isometry from $L^2(N)$ into $L^2(G)$. In this paper we give an explicit construction of admissible vectors in the case where $G$ is not unimodular and the stabilizers in $H$ of its action on $\hat N$ are almost everywhere trivial. In this situation we prove orthogonality relations and we construct an explicit decomposition of $L^2(G)$ into $G$-invariant, multiplicity-free subspaces each of which is the image of a wavelet transform . We also show that, with the assumption of (almost-everywhere) trivial stabilizers, non-unimodularity is necessary for the existence of admissible vectors. Categories:22E27, 22E30

69. CJM 2007 (vol 59 pp. 795)

Jaworski, Wojciech; Neufang, Matthias
 The Choquet--Deny Equation in a Banach Space Let $G$ be a locally compact group and $\pi$ a representation of $G$ by weakly$^*$ continuous isometries acting in a dual Banach space $E$. Given a probability measure $\mu$ on $G$, we study the Choquet--Deny equation $\pi(\mu)x=x$, $x\in E$. We prove that the solutions of this equation form the range of a projection of norm $1$ and can be represented by means of a Poisson formula'' on the same boundary space that is used to represent the bounded harmonic functions of the random walk of law $\mu$. The relation between the space of solutions of the Choquet--Deny equation in $E$ and the space of bounded harmonic functions can be understood in terms of a construction resembling the $W^*$-crossed product and coinciding precisely with the crossed product in the special case of the Choquet--Deny equation in the space $E=B(L^2(G))$ of bounded linear operators on $L^2(G)$. Other general properties of the Choquet--Deny equation in a Banach space are also discussed. Categories:22D12, 22D20, 43A05, 60B15, 60J50

70. CJM 2007 (vol 59 pp. 148)

Muić, Goran
 On Certain Classes of Unitary Representations for Split Classical Groups In this paper we prove the unitarity of duals of tempered representations supported on minimal parabolic subgroups for split classical $p$-adic groups. We also construct a family of unitary spherical representations for real and complex classical groups Categories:22E35, 22E50, 11F70

71. CJM 2006 (vol 58 pp. 1229)

Henniart, Guy; Lemaire, Bertrand
 IntÃ©grales orbitales tordues sur $\GL(n,F)$ et corps locaux proches\,: applications Soient $F$ un corps commutatif localement compact non archim\'edien, $G=\GL (n,F)$ pour un entier $n\geq 2$, et $\kappa$ un caract\ere de $F^\times$ trivial sur $(F^\times)^n$. On prouve une formule pour les $\kappa$-int\'egrales orbitales r\'eguli\eres sur $G$ permettant, si $F$ est de caract\'eristique $>0$, de les relever \a la caract\'eristique nulle. On en d\'eduit deux r\'esultats nouveaux en caract\'eristique $>0$\,: le lemme fondamental'' pour l'induction automorphe, et une version simple de la formule des traces tordue locale d'Arthur reliant $\kappa$-int\'egrales orbitales elliptiques et caract\eres $\kappa$-tordus. Cette formule donne en particulier, pour une s\'erie $\kappa$-discr\ete de $G$, les $\kappa$-int\'egrales orbitales elliptiques d'un pseudo-coefficient comme valeurs du caract\ere $\kappa$-tordu. Keywords:corps local, reprÃ©sentation lisse, intÃ©grale orbitale tordue, induction automorphe, lemme fondamental, formule des traces locale, pseudo-coefficientCategory:22E50

72. CJM 2006 (vol 58 pp. 1203)

Heiermann, Volker
 Orbites unipotentes et pÃ´les d'ordre maximal de la fonction $\mu$ de Harish-Chandra Dans un travail ant\'erieur, nous avions montr\'e que l'induite parabolique (normalis\'ee) d'une repr\'esentation irr\'eductible cuspidale $\sigma$ d'un sous-groupe de Levi $M$ d'un groupe $p$-adique contient un sous-quotient de carr\'e int\'egrable, si et seulement si la fonction $\mu$ de Harish-Chandra a un p\^ole en $\sigma$ d'ordre \'egal au rang parabolique de $M$. L'objet de cet article est d'interpr\'eter ce r\'esultat en termes de fonctorialit\'e de Langlands. Categories:11F70, 11F80, 22E50

73. CJM 2006 (vol 58 pp. 1095)

Sakellaridis, Yiannis
 A Casselman--Shalika Formula for the Shalika Model of $\operatorname{GL}_n$ The Casselman--Shalika method is a way to compute explicit formulas for periods of irreducible unramified representations of $p$-adic groups that are associated to unique models (i.e., multiplicity-free induced representations). We apply this method to the case of the Shalika model of $GL_n$, which is known to distinguish lifts from odd orthogonal groups. In the course of our proof, we further develop a variant of the method, that was introduced by Y. Hironaka, and in effect reduce many such problems to straightforward calculations on the group. Keywords:Casselman--Shalika, periods, Shalika model, spherical functions, Gelfand pairsCategories:22E50, 11F70, 11F85

74. CJM 2006 (vol 58 pp. 897)

Courtès, François
 Distributions invariantes sur les groupes rÃ©ductifs quasi-dÃ©ployÃ©s Soit $F$ un corps local non archim\'edien, et $G$ le groupe des $F$-points d'un groupe r\'eductif connexe quasi-d\'eploy\'e d\'efini sur $F$. Dans cet article, on s'int\'eresse aux distributions sur $G$ invariantes par conjugaison, et \a l'espace de leurs restrictions \a l'alg\ebre de Hecke $\mathcal{H}$ des fonctions sur $G$ \a support compact biinvariantes par un sous-groupe d'Iwahori $I$ donn\'e. On montre tout d'abord que les valeurs d'une telle distribution sur $\mathcal{H}$ sont enti\erement d\'etermin\'ees par sa restriction au sous-espace de dimension finie des \'el\'ements de $\mathcal{H}$ \a support dans la r\'eunion des sous-groupes parahoriques de $G$ contenant $I$. On utilise ensuite cette propri\'et\'e pour montrer, moyennant certaines conditions sur $G$, que cet espace est engendr\'e d'une part par certaines int\'egrales orbitales semi-simples, d'autre part par les int\'egrales orbitales unipotentes, en montrant tout d'abord des r\'esultats analogues sur les groupes finis. Keywords:reductive $p$-adic groups, orbital integrals, invariant distributionsCategories:22E35, 20G40

75. CJM 2006 (vol 58 pp. 673)

Bart, Anneke; Scannell, Kevin P.
 The Generalized Cuspidal Cohomology Problem Let $\Gamma \subset \SO(3,1)$ be a lattice. The well known \emph{bending deformations}, introduced by \linebreak Thurston and Apanasov, can be used to construct non-trivial curves of representations of $\Gamma$ into $\SO(4,1)$ when $\Gamma \backslash \hype{3}$ contains an embedded totally geodesic surface. A tangent vector to such a curve is given by a non-zero group cohomology class in $\H^1(\Gamma, \mink{4})$. Our main result generalizes this construction of cohomology to the context of branched'' totally geodesic surfaces. We also consider a natural generalization of the famous cuspidal cohomology problem for the Bianchi groups (to coefficients in non-trivial representations), and perform calculations in a finite range. These calculations lead directly to an interesting example of a link complement in $S^3$ which is not infinitesimally rigid in $\SO(4,1)$. The first order deformations of this link complement are supported on a piecewise totally geodesic $2$-complex. Categories:57M50, 22E40
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