Soit $F$ un corps de nombres et soit $E$ une extension cyclique de $F$, de degré $d$. L’induction automorphe associe à une représentation automorphe cuspidale $\tau$ de ${\mathrm{GL}}_m\left({𝔸}_E\right)$ une représentation automorphe $\pi$ de ${\mathrm{GL}}_{md}\left({𝔸}_F\right)$, induite de cuspidale. La représentation $\pi$ est caractérisée par le fait qu’à presque toute place $v$ de $F$, le facteur $L({\pi }_v,s)$ est le produit des facteurs $L({\tau }_w,s)$, $w$ parcourant les places de $E$ au–dessus de $v$. Par la correspondance conjecturale de Langlands, cette opération doit correspondre à l’induction, de $E$ à $F$, des...

Let G be a non-discrete locally compact group, A(G) the Fourier algebra of G, VN(G) the von Neumann algebra generated by the left regular representation of G which is identified with A(G)*, and WAP(Ĝ) the space of all weakly almost periodic functionals on A(G). We show that there exists a directed family ℋ of open subgroups of G such that: (1) for each H ∈ ℋ, A(H) is extremely non-Arens regular; (2) $VN\left(G\right)={\bigcup }_{H\in \mathscr{H}}VN\left(H\right)$ and $VN\left(G\right)/WAP\left(Ĝ\right)={\bigcup }_{H\in \mathscr{H}}[VN\left(H\right)/WAP\left(Ĥ\right)]$; (3) $A\left(G\right)={\bigcup }_{H\in \mathscr{H}}A\left(H\right)$ and it is a WAP-strong inductive union in the sense that the unions in (2) are strongly...

We construct infinite measure preserving and nonsingular rank one ${\mathbb{Z}}^d$-actions. The first example is ergodic infinite measure preserving but with nonergodic, infinite conservative index, basis transformations; in this case we exhibit sets of increasing finite and infinite measure which are properly exhaustive and weakly wandering. The next examples are staircase rank one infinite measure preserving ${\mathbb{Z}}^d$-actions; for these we show that the individual basis transformations have conservative ergodic Cartesian...

In this paper, we construct a hyperkähler structure on the complexification ${𝒪}^{ℂ}$ of any Hermitian symmetric affine coadjoint orbit $𝒪$ of a semi-simple $L^{*}$-group of compact type, which is compatible with the complex symplectic form of Kirillov-Kostant-Souriau and restricts to the Kähler structure of $𝒪$. By a relevant identification of the complex orbit ${𝒪}^{ℂ}$ with the cotangent space $T𝒪$ of $𝒪$ induced by Mostow’s decomposition theorem, this leads to the existence of a hyperkähler structure on $T𝒪$ compatible with...

Let L be the full laplacian on the Heisenberg group ${ℍ}^n$ of arbitrary dimension n. Then for $f\in L^2\left({ℍ}^n\right)$ such that ${(I-L)}^{s/2}f\in L^2\left({ℍ}^n\right)$, s > 3/4, for a $\varphi \in C_c\left({ℍ}^n\right)$ we have ${ʃ}_{{ℍ}^n}\left|\varphi \left(x\right)\right|su{p}_{0<t\le 1}{\left|e^{(\surd -1)tL}f\left(x\right)\right|}^{2}dx\le C_{\varphi }\parallel f{\parallel }_{W^s}^2$. On the other hand, the above maximal estimate fails for s < 1/4. If Δ is the sublaplacian on the Heisenberg group ${ℍ}^n$, then for every s < 1 there exists a sequence $f_n\in L^2\left({ℍ}^n\right)$ and $C_n>0$ such that ${(I-L)}^{s/2}{f}_n\in L^2\left({ℍ}^n\right)$ and for a $\varphi \in C_c\left({ℍ}^n\right)$ we have ${ʃ}_{{ℍ}^n}\left|\varphi \left(x\right)\right|su{p}_{0<t\le 1}{\left|e^{(\surd -1)t\Delta }{f}_n\left(x\right)\right|}^{2}dx\ge C_n\parallel f_n{\parallel }_{W^s}^2,li{m}_{n\to \infty }{C}_n=+\infty$.