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Structure de certaines C * -algèbres associées aux réseaux de PSL 2 ( )

François Pierrot (2002)

Annales de l’institut Fourier

En utilisant la structure infinitésimale des représentations unitaires irréductibles de PSL 2 ( ) , nous donnons une description complète de certaines C * - algèbres associées aux réseaux de PSL 2 ( ) , répondant ainsi à certaines questions de Bekka–de La Harpe–Valette.

Structure of the kernel of higher spin Dirac operators

Martin Plechšmíd (2001)

Commentationes Mathematicae Universitatis Carolinae

Polynomials on n with values in an irreducible Spin n -module form a natural representation space for the group Spin n . These representations are completely reducible. In the paper, we give a complete description of their decompositions into irreducible components for polynomials with values in a certain range of irreducible modules. The results are used to describe the structure of kernels of conformally invariant elliptic first order systems acting on maps on n with values in these modules.

Subalgebras generated by extreme points in Fourier-Stieltjes algebras of locally compact groups

Michael Yin-hei Cheng (2011)

Studia Mathematica

Let G be a locally compact group, G* be the set of all extreme points of the set of normalized continuous positive definite functions of G, and a(G) be the closed subalgebra generated by G* in B(G). When G is abelian, G* is the set of Dirac measures of the dual group Ĝ, and a(G) can be identified as l¹(Ĝ). We study the properties of a(G), particularly its spectrum and its dual von Neumann algebra.

Sub-Laplacian with drift in nilpotent Lie groups

Camillo Melzi (2003)

Colloquium Mathematicae

We consider the heat kernel ϕ t corresponding to the left invariant sub-Laplacian with drift term in the first commutator of the Lie algebra, on a nilpotent Lie group. We improve the results obtained by G. Alexopoulos in [1], [2] proving the “exact Gaussian factor” exp(-|g|²/4(1+ε)t) in the large time upper Gaussian estimate for ϕ t . We also obtain a large time lower Gaussian estimate for ϕ t .

Sub-Laplacians of holomorphic L p -type on exponential Lie groups

Detlef Müller (2002)

Atti della Accademia Nazionale dei Lincei. Classe di Scienze Fisiche, Matematiche e Naturali. Rendiconti Lincei. Matematica e Applicazioni

In this survey article, I shall give an overview on some recent developments concerning the L p -functional calculus for sub-Laplacians on exponential solvable Lie groups. In particular, I shall give an outline on some recent joint work with W. Hebisch and J. Ludwig on sub-Laplacians which are of holomorphic L p -type, in the sense that every L p -spectral multiplier for p 2 will be holomorphic in some domain.

Sugli insiemi piccoli in un gruppo

Antonio Vitolo, Umberto Zannier (1988)

Atti della Accademia Nazionale dei Lincei. Classe di Scienze Fisiche, Matematiche e Naturali. Rendiconti Lincei. Matematica e Applicazioni

Un insieme S in un gruppo G si dice piccolo se esistono infiniti traslati di S a due a due disgiunti. In questa nota dimostriamo in modo elementare che, sotto opportune ipotesi, G non può essere l'unione di un numero finito di insiemi piccoli (e una generalizzazione di questo risultato).

Summable families in nuclear groups

Wojciech Banaszczyk (1993)

Studia Mathematica

Nuclear groups form a class of abelian topological groups which contains LCA groups and nuclear locally convex spaces, and is closed with respect to certain natural operations. In nuclear locally convex spaces, weakly summable families are strongly summable, and strongly summable are absolutely summable. It is shown that these theorems can be generalized in a natural way to nuclear groups.

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