Vladimir V. Uspenskij
For every Tikhonov space $X$ the free abelian topological group $A(X)$ and the free locally convex vector space $L(X)$ admit a topologically faithful unitary representation. For compact spaces $X$ this is due to Jorge Galindo.
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We use $t$-structures on the homotopy category $K^b(R-mod)$ for an artin algebra $R$ and Watts' representability theorem to give an existence proof for Auslander-Reiten sequences of $R$-modules.
Unitary representations attached to parabolic subgroups: the case of abelian unipotent radical
本文研究了在几何参数空间源于 Levi 子群作用于抛物子代数阿贝尔幂零根基的情形下，对 Lusztig 幂零表示范畴中具有整数无穷小特征的酉表示进行分类，并将其组织成微局部 Arthur 包，作为验证相关酉表示猜想描述的测试用例。
Let V_* be the normalized unitary subgroup of the modular group algebra FG of a finite p-group G over a finite field F with the classical involution *. We investigate the isomorphism problem for the group V_*, that asks when the group V_* is determined by its group algebra FG. We confirm it for classes of finite abelian p-groups, 2-groups of maximal class and non-abelian 2-groups of order at most 16.
Suppose that $H$ is a closed subgroup of a locally compact group $G$. We show that a unitary representation $U$ of $H$ is the restriction of a unitary representation of $G$ if and only if a dual representation $\hat U$ of a crossed product $C^*(G)\rtimes (G/H)$ is regular in an appropriate sense. We then discuss the problem of deciding whether a given representation is regular; we believe that this problem will prove to be an interesting test question in non-abelian duality for crossed products of $C^*$-algebras.
Representations of the unitary group SU(2,1) in Fourier term modules
本文研究 SU(2,1) 上由自守形式傅里叶展开产生的傅里叶项模，允许指数增长以处理广义自守形式，完整刻画了所有傅里叶项模的子模结构及其对傅里叶展开的影响。
Point-group filtering in unitary coupled-cluster ansätze: exact criticality under the Abelian filter, freeness measured near equilibrium under the full group
本文研究了非阿贝尔分子点群中对称适应变分量子本征值求解器（VQE）的局限性，指出阿贝尔子群限制导致多维不可约表示的虚假分裂，并通过李代数层面的分析证明了动态李代数被限制在阿贝尔子代数中，从而导致状态流形受限于测度为零的托罗斯，同时指出数值障碍需要补充完整非对角线生成元和独立参数化交叉分量激发。
Using Harish-Chandra induction and restriction, we construct a categorical action of a Kac-Moody algebra on the category of unipotent representations of finite unitary groups in non-defining characteristic. We show that the decategorified representation is naturally isomorphic to a direct sum of level 2 Fock spaces. From our construction we deduce that the Harish-Chandra branching graph coincide with the crystal graph of these Fock spaces, solving a recent conjecture of Gerber-Hiss-Jacon. We also obtain derived equivalences between blocks, yielding Broué's abelian defect groups conjecture for …
This is a largely expository article based on our previous work on arithmetic diagonal cycles on unitary Shimura varieties. We define a class of Shimura varieties closely related to unitary groups which represent a moduli problem of abelian varieties with additional structure, and which admit interesting algebraic cycles. We generalize to arbitrary signature type the results of our previous work valid under special signature conditions. We compare our Shimura varieties with other unitary Shimura varieties.
Let F be the field of two elements and G a finite abelian 2-group with an involutory automorphism. The extension of this automorphism to the group algebra FG is called an involutory involution. This determines the groups of unitary and symmetric normalized units of FG. We calculate the orders and the invariants of these subgroups.
Let ${\mathcal O}$ be an involutive discrete valuation ring with residue field of characteristic not 2. Let $A$ be a quotient of ${\mathcal O}$ by a nonzero power of its maximal ideal and let $*$ be the involution that $A$ inherits from ${\mathcal O}$. We consider various unitary groups ${\mathcal U}_m(A)$ of rank $m$ over $A$, depending on the nature of $*$ and the equivalence type of the underlying hermitian or skew hermitian form. Each group ${\mathcal U}_m(A)$ gives rise to a Weil representation. In this paper, we give a Clifford theory description of all irreducible components of the Weil…
We provide descriptions for the moduli spaces $\text{Rep}(Γ, PU(m))$, where $Γ$ is any finitely generated abelian group and $PU(m)$ is the group of $m\times m$ projective unitary matrices. As an application we show that for any connected CW-complex $X$ with $π_1(X)\cong \mathbf{Z}^n$, the natural map $π_0(\text{Rep}(π_1(X), PU(m)))\to [X, BPU(m)]$ is injective, hence providing a complete enumeration of the isomorphism classes of flat principal $PU(m)$-bundles over $X$.
We initiate a study of infinite tensor products of projective unitary representations of a discrete group G. Special attention is given to regular representations twisted by 2-cocycles and to projective representations associated with CCR-representations of bilinear maps. Detailed computations are presented in the case where G is a finitely generated free abelian group. We also discuss an extension problem about product type actions of G, where the projective representation theory of G plays a central role.
We generalize the work of DeBacker and Reeder to the case of unitary groups split by a tame extension. The approach is broadly similar and the restrictions on the parameter the same, but many of the details of the arguments differ. Let $G$ be a unitary group defined over a local field $K$ and splitting over a tame extension $E/K$. Given a Langlands parameter $φ: \mathcal{W}_K \rightarrow {^L G}$ that is tame, discrete and regular, we give a natural construction of an $L$-packet $Π_φ$ associated to $φ$, consisting of representations of pure inner forms of $G(K)$ and parametrized by the characte…
We investigate the structure of subspaces of a Hilbert space that are invariant under unitary representations of a discrete group. We work with square integrable representations, and we show that they are those for which we can construct an isometry intertwining the representation with the right regular representation, that we call a Helson map. We then characterize invariant subspaces using the Helson map, and provide general characterizations of Riesz and frame sequences of orbits. These results extend to the nonabelian setting several known results for abelian groups. They also extend to co…
A finite sampling theory associated with a unitary representation of a finite non Abelian group $\mathbf{G}$ on a Hilbert space is stablished. The non Abelian group $\mathbf{G}$ is a knit product $\mathbf{N}\bowtie \mathbf{H}$ of two finite subgroups $\mathbf{N}$ and $\mathbf{H}$. Sampling formulas where the samples are indexed by either $\mathbf{N}$ or $\mathbf{H}$ are obtained. Using suitable expressions for the involved samples, the problem is reduced to obtain dual frames in the Hilbert space $\ell^2(\mathbf{G})$ having a unitary invariance property; this is done by using matrix analysis t…
We characterize orthonormal bases, Riesz bases and frames which arise from the action of a countable discrete group $Γ$ on a single element $ψ$ of a given Hilbert space $\mathcal{H}$. As $Γ$ might not be abelian, this is done in terms of a bracket map taking values in the $L^1$-space associated to the group von Neumann algebra of $Γ$. Our result generalizes recent work for LCA groups. In many cases, the bracket map can be computed in terms of a noncommutative form of the Zak transform.
In this paper we prove the blockwise Alperin weight conjecture for finite special linear and unitary groups, for finite groups with abelian Sylow $3$-subgroups, and verify the inductive blockwise Alperin weight condition for certain cases of groups of type $\mathsf A$. We also give a classification for the 2-blocks of special linear and unitary groups.
For $φ$ a normalized positive definite function on a locally compact abelian group $G$, we consider on the one hand the unitary representation $π_φ$ associated to $φ$ by the GNS construction, on the other hand the probability measure $μ_φ$ on the Pontryagin dual $\hat{G}$ provided by Bochner's theorem. We give necessary and sufficient conditions for the vanishing of 1-cohomology $H^1(G,π_φ)$ and reduced 1-cohomology $\bar{H}^1(G,π_φ)$. For example, $\bar{H}^1(G,π_φ)=0$ if and only if either $Hom(G,\mathbb{C})=0$ or $μ_φ(1_G)=0$, where $1_G$ is the trivial character of $G$.
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