Projective Representations and Pure Pseudorepresentations of Hermitian Symmetric Simple Lie Groups

It is shown that an arbitrary irreducible continuous unitary projective representation of a simple Hermitian symmetric Lie group is generated by a strongly continuous pure unitary pseudorepresentation of the adjoint group of the Lie group.__________Translated from Matematicheskie Zametki, vol. 78, no. 1, 2005, pp. 140–146.Original Russian Text Copyright © 2005 by A. I. Shtern.     

Inhomogeneous Lévy Processes in Lie Groups and Homogeneous Spaces

We obtain a representation of an inhomogeneous Lévy process in a Lie group or a homogeneous space in terms of a drift, a matrix function and a measure function. Since the stochastic continuity is not assumed, our result generalizes the well-known Lévy–Itô representation for stochastic continuous processes with independent increments in ? ^d and its extension to Lie groups.     

Separate and joint analyticity in Lie groups representations

We prove that for any Lie group there exists a basis of its Lie Algebra in which for any representation of the Lie group in a Hilbert space, a vector which is analytic for every operator representing that basis is an analytic vector for the representation.     

A quantum analogue of Hunt's representation theorem for the generator of convolution semigroups on Lie groups

Summary In quantum mechanics certain operator-valued measures are introduced, called instruments, which are an analogue of the probability measures of classical probability theory. As in the classical case, it is interesting to study convolution semigroups of instruments on groups and the associated semigroups of probability operators. In this paper the case is considered of a finite-dimensional Hilbert space (n-level quantum system) and of instruments defined on a finite-dimensional Lie group. Then, the generator of a continuous semigroup of (quantum) probability operators is characterized. In this way a quantum analogue of Hunt's representation theorem for the generator of convolution semigroups on Lie groups is obtained.     

Optimal Control and Geodesics on Quadratic Matrix Lie Groups

The purpose of this paper is to extend the symmetric representation of the rigid body equations from the group SO (n) to other groups. These groups are matrix subgroups of the general linear group that are defined by a quadratic matrix identity. Their corresponding Lie algebras include several classical semisimple matrix Lie algebras. The approach is to start with an optimal control problem on these groups that generates geodesics for a left-invariant metric. Earlier work by Bloch, Crouch, Marsden, and Ratiu defines the symmetric representation of the rigid body equations, which is obtained by solving the same optimal control problem in the particular case of the Lie group SO (n). This paper generalizes this symmetric representation to a wider class of matrix groups satisfying a certain quadratic matrix identity. We consider the relationship between this symmetric representation of the generalized rigid body equations and the generalized rigid body equations themselves. A discretization of this symmetric representation is constructed making use of the symmetry, which in turn give rise to numerical algorithms to integrate the generalized rigid body equations for the given class of matrix Lie groups. Dedicated to Professor Arieh Iserles on the Occasion of his Sixtieth Birthday.     

Differentiability of continuous homomorphisms between smooth loops

It is a well-known fact that a continuous homomorphism between Lie groups is analytic. We prove a similar result (Thm. 1.8) for continuous homomorphisms of differentiable left or right loops in section 1 of this paper. Section 2 deals with images and kernels of such homomorphisms. Again, the results obtained are quite analogous to the Lie group case. The paper ends with applications of Theorem 1.8. For example, it turns out that the group of continuous automorphisms of a smooth generalized polygon is a Lie transformation group with respect to the compact-open topology.     

Symmetric nonself-adjoint operators in an enveloping algebra

Nelson and Stinespring proved that in any unitary representation of a Lie group with compact Lie algebra the representation of Hermitian elements in the enveloping algebra are essentially self-adjoint. If the Lie algebra is noncompact, we construct in its enveloping algebra a Hermitian element u such that in any locally faithful unitary representation the representative of u has no self-adjoint extension.     

A Low Complexity Lie Group Method on the Stiefel Manifold

A low complexity Lie group method for numerical integration of ordinary differential equations on the orthogonal Stiefel manifold is presented. Based on the quotient space representation of the Stiefel manifold we provide a representation of the tangent space suitable for Lie group methods. According to this representation a special type of generalized polar coordinates (GPC) is defined and used as a coordinate map. The GPC maps prove to adapt well to the Stiefel manifold. For the n×k matrix representation of the Stiefel manifold the arithmetic complexity of the method presented is of order nk ², and for nk this leads to huge savings in computation time compared to ordinary Lie group methods. Numerical experiments compare the method to a standard Lie group method using the matrix exponential, and conclude that on the examples presented, the methods perform equally on both accuracy and maintaining orthogonality.     

Unitary representations of unimodular Lie groups in Bergman spaces

For an arbitrary unimodular Lie group G, we construct strongly continuous unitary representations in the Bergman space of a strongly pseudoconvex neighborhood of G in the complexification of its underlying manifold. These representation spaces are infinite-dimensional and have compact kernels. In particular, the Bergman spaces of these natural manifolds are infinite-dimensional.     

Convexity and unitary representations of nilpotent Lie groups

Summary The moment map of symplectic geometry is extended to associate to any unitary representation of a nilpotent Lie group aG-invariant subset of the dual of the Lie algebra. We prove that this subset is the closed conex hull of the Kirillov orbit of the representation.Supported by NSERC research grant no. A7918     

On the supports of absolutely continuous Gauss measures on connected Lie groups

The behaviour of the supports of an absolutely continuous Gauss semigroup on certain Lie groups is discussed. It is shown that on a connected nilpotent Lie group any absolutely continuous Gauss semigroup has full supports but on compact connected Lie groups which are not Abelian there exist absolutely continuous Gauss semigroups which do not have common supports.     

The moment mapping for unitary representations

For any unitary representation of an arbitrary Lie group I construct a moment mapping from the space of smooth vectors of the representation into the dual of the Lie algebra. This moment mapping is equivariant and smooth. For the space of analytic vectors the same construction is possible and leads to a real analytic moment mapping.     

Riccati equations and Lie series

Lie series and a special matrix notation for first-order differential operators are used to show that the Lie group properties of matrix Riccati equations arise in a natural way. The Lie series notation makes it evident that the solutions of a matrix Riccati equation are curves in a group of nonlinear transformations that is a generalization of the linear fractional transformations familiar from the classical complex analysis. It is easy to obtain a linear representation of the Lie algebra of the nonlinear group of transformations and then this linearization leads directly to the standard linearization of the matrix Riccati equations. We note that the matrix Riccati equations considered here are of the general rectangular type.     

Irreducible connected Lie subgroups of Gl n (R) are closed

IfG is a connected real Lie group and π:G→Aut (V) a continuous irreducible finite-dimensional real representation then we show that π(G) is closed in Aut(V). A similar result is valid in the complex case.     

Classification of Similarity Solutions for Inviscid Burgers’ Equation

Using the basic Lie symmetry method, we find the most general Lie point symmetries group of the inviscid Burgers’ equation. Looking at the adjoint representation of the obtained symmetry group on its Lie algebra, we find the preliminary classification of its group-invariant solutions. The latter provides new exact solutions for the inviscid Burgers’ equation.     

Twisted cocycles of lie algebras and corresponding invariant functions

We consider finite-dimensional complex Lie algebras. Using certain complex parameters we generalize the concept of cohomology cocycles of Lie algebras. A special case is generalization of 1-cocycles with respect to the adjoint representation - so called (α,β,γ)-derivations. Parametric sets of spaces of cocycles allow us to define complex functions which are invariant under Lie isomorphisms. Such complex functions thus represent useful invariants - we show how they classify three and four-dimensional Lie algebras as well as how they apply to some eight-dimensional one-parametric nilpotent continua of Lie algebras. These functions also provide necessary criteria for existence of 1-parametric continuous contraction.     

本刊英文版Vol.32(2016),No.8论文摘要（英文）

正A New Functor from D_5-Mod to E_6-Mod Xiao Ping XU Abstract We find a new representation of the simple Lie algebra of type E_6 on the polynomial algebra in 16 variables,which gives a fractional representation of the corresponding Lie group on 16-dimensional space.Using this representation and Shen's idea of mixed product,we construct a new functor from D_5-Mod to E_6-Mod.A condition for the functor to map a     

Space of orbits of a three-dimensional simple compact linear Lie group

An upper estimate for the codimension of the subspace of points with finite orbits for a representation of a three-dimensional simple compact Lie group whose quotient is a manifold is obtained.