No Arabic abstract
Let $pi$ be a genuine cuspidal representation of the metaplectic group of rank $n$. We consider the theta lifts to the orthogonal group associated to a quadratic space of dimension $2n+1$. We show a case of regularised Rallis inner product formula that relates the pairing of theta lifts to the central value of the Langlands $L$-function of $pi$ twisted by a character. The bulk of this article focuses on proving a case of regularised Siegel-Weil formula, on which the Rallis inner product formula is based and whose proof is missing in the literature.
This paper initiates a study into the contribution to the trace provided by the conjugacy classes.
Mean dimension is a topological invariant of dynamical systems, which originates with Mikhail Gromov in 1999 and which was studied with deep applications around 2000 by Elon Lindenstrauss and Benjamin Weiss within the framework of amenable group actions. Let a countable discrete amenable group $G$ act continuously on compact metrizable spaces $X$ and $Y$. Consider the product action of $G$ on the product space $Xtimes Y$. The product inequality for mean dimension is well known: $mathrm{mdim}(Xtimes Y,G)lemathrm{mdim}(X,G)+mathrm{mdim}(Y,G)$, while it was unknown for a long time if the product inequality could be an equality. In 2019, Masaki Tsukamoto constructed the first example of two different continuous actions of $G$ on compact metrizable spaces $X$ and $Y$, respectively, such that the product inequality becomes strict. However, there is still one longstanding problem which remains open in this direction, asking if there exists a continuous action of $G$ on some compact metrizable space $X$ such that $mathrm{mdim}(Xtimes X,G)<2cdotmathrm{mdim}(X,G)$. We solve this problem. Somewhat surprisingly, we prove, in contrast to (topological) dimension theory, a rather satisfactory theorem: If an infinite (countable discrete) amenable group $G$ acts continuously on a compact metrizable space $X$, then we have $mathrm{mdim}(X^n,G)=ncdotmathrm{mdim}(X,G)$, for any positive integer $n$. Our product formula for mean dimension, together with the example and inequality (stated previously), eventually allows mean dimension of product actions to be fully understood.
A bounded linear operator $T$ on a Hilbert space is said to be homogeneous if $varphi(T)$ is unitarily equivalent to $T$ for all $varphi$ in the group M{o}b of bi-holomorphic automorphisms of the unit disc. A projective unitary representation $sigma$ of M{o}b is said to be associated with an operator T if $varphi(T)= sigma(varphi)^star T sigma(varphi)$ for all $varphi$ in M{o}b. In this paper, we develop a M{o}bius equivariant version of the Sz.-Nagy--Foias model theory for completely non-unitary (cnu) contractions. As an application, we prove that if T is a cnu contraction with associated (projective unitary) representation $sigma$, then there is a unique projective unitary representation $hat{sigma}$, extending $sigma$, associated with the minimal unitary dilation of $T$. The representation $hat{sigma}$ is given in terms of $sigma$ by the formula $$ hat{sigma} = (pi otimes D_1^+) oplus sigma oplus (pi_star otimes D_1^-), $$ where $D_1^pm$ are the two Discrete series representations (one holomorphic and the other anti-holomorphic) living on the Hardy space $H^2(mathbb D)$, and $pi, pi_star$ are representations of M{o}b living on the two defect spaces of $T$ defined explicitly in terms of $sigma$. Moreover, a cnu contraction $T$ has an associated representation if and only if its Sz.-Nagy--Foias characteristic function $theta_T$ has the product form $theta_T(z) = pi_star(varphi_z)^* theta_T(0) pi(varphi_z),$ $zin mathbb D$, where $varphi_z$ is the involution in M{o}b mapping $z$ to $0.$ We obtain a concrete realization of this product formula %the two representations $pi_star$ and $pi$ for a large subclass of homogeneous cnu contractions from the Cowen-Douglas class.
We treat the problem of normally ordering expressions involving the standard boson operators a, a* where [a,a*]=1. We show that a simple product formula for formal power series - essentially an extension of the Taylor expansion - leads to a double exponential formula which enables a powerful graphical description of the generating functions of the combinatorial sequences associated with such functions - in essence, a combinatorial field theory. We apply these techniques to some examples related to specific physical Hamiltonians.
Let G be a semisimple Lie group and H a uniform lattice in G. The Selberg trace formula is an equality arising from computing in two different ways the traces of convolution operators on the Hilbert space L^2(G/H) associated to test functions. In this paper we present a cohomological interpretation of the trace formula involving the K-theory of the maximal group C*-algebras of G and H. As an application, we exploit the role of group C*-algebras as recipients of higher indices of elliptic differential operators and we obtain the index theoretic version of the Selberg trace formula developed by Barbasch and Moscovici from ours.