Questions tagged [lie-groups]
Lie Groups are Groups that are additionally smooth manifolds such that the multiplication and the inverse maps are smooth.
3,059 questions
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Iwasawa Decomposition for Matrices [closed]
I was asked to prove that if
$$ T_{n}^{+}(\mathbb{R}) \subseteq M_{n}(\mathbb{R})$$
denotes the set of upper triangular matrices with positive diagonal entries, then prove that the multiplication ...
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A decomposition of the "spin representation" of SL(2)
Let us take an N-dimensional (N odd) irreducible representation V of SL(2,R).
It is known that (e.g., Lie groups and Lie algebras III by Vinberg and Onischik, 1994 p. 94) in V there is an invariant ...
- 1,765
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Can one understand the Kelvin transform conceptually?
Let $U = \mathbf{R}^n - \{ 0 \}$, $n > 2$ and consider for a function $f \in C^2(U)$ the Kelvin transform
$$f^\star(x) = r^{2-n} f\left(\frac{x}{r^2}\right),$$
where $r = \lvert x \rvert$. One ...
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Closed subgroups of GL(n)
Let's say I want to prove that a closed subgroup of GL(n,R) or GL(n,C) is a Lie group, with an atlas given by exponential of matrices (restricted to an appropriate subalgebra of gl(n)), without using ...
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Measure on orbits of $N$ under conjugation by $H$
Let $G$ be a locally compact topological group with closed subgroups $H, N$ and $H$ normalizing $N$. Then $H$ acts continuously on $N$ by conjugation. If it will help, assume that $N$ is nilpotent, ...
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quasi-minuscule representations
Wich representations of $F_{4}$, $E_{8}$ and $G_{2}$ are quasi-minuscule?
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Simultaneous integral equation on $SU(n)$
Consider a smooth curve $U_s:[0,T] \rightarrow SU(4)$ which solves:
$\frac{d U_s}{ds} = (a + w(s)b)U_s$
for some given $a,b \in \mathfrak{su}(4)$ (which generate $\mathfrak{su}(n)$) and a smooth ...
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On closed totally disconnected subgroups of connected real Lie groups
So the following statement seems to be obvious but I don't see how to prove it:
Q: How does one prove that a closed totally disconnected subgroup of a connected real Lie group is discrete?
Note that ...
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Does a free action always induce a diffeomorphism?
Suppose that $G$ is a Lie group with a transitive action on a smooth manifold $M$. The regular theory of Lie groups tells us that $G$ and $M$ are diffeomorphic if the isotropy group is trivial.
The ...
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Maximal compact subgroups of a semisimple Lie group are conjugate
I'm trying to go through the proof that all maximal compact subgroups of a semisimple Lie group $G$ are conjugate. I know that a possible proof follows the following steps:
Take one maximal compact ...
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The logarith map as a contraction [closed]
Two Questions:
(1) Under what conditions(if any) can the logarithm map from a point on a Riemannian manifold, $q_1\in Q$, to the Tangent Space $T_{q_0}Q$, locally, be a contraction mapping?
Or more ...
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Can SO_n(R) be approximated arbitrarily well using a discrete subgroup?
Let $G := SO_n(R)$ be equipped with the Euclidean metric on vectors of length $n^2$. Is it true that for any $\epsilon >0$, there is a finite subgroup of $G$ which intersects every metric ball of ...
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Linear subspaces in cones over orthogonal groups
Consider the orthogonal group $G=O(n)$ as a subset of the vector space of $n\times n$ real matrices. Let $C=C(G)$ denote the Euclidean cone over $G$, i.e., the space of matrices of the form $tA, A\in ...
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Noncompact dual of $\mathrm{Spin}(2n)$ corresponding to $\mathfrak{so}^*(2n)$
Let $U=\mathrm{Spin}(2n)$, which is a simply connected compact simple Lie group, and let $\mathfrak{u}_0=\mathfrak{so}(2n)$, the Lie algebra of $U$. If $\mathfrak{g}_0$ is a noncompact dual of $\...
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Equivariant $K$-theory, singular vectors, and flag manifolds
For a homogeneous space $M = G/B$, with $G$ a (complex) semi-simple Lie group, it is very well-known that equivariant vector bundles $E$ over $M$ correspond to representations $(V_{\lambda},\lambda)$ ...
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Principal bundle: A criterion
I am referring to page 300 of Okonek et al. book "Vector Bundles on Complex Projective Spaces" (1988.)
Let $G=GL_n(\mathbb{C})$ act holomorphically and freely on a complex manifold $X$. ...
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Orbit structure of linear representations of complex Lie groups
Let $G$ be a semisimple complex Lie group (or perhaps a reductive algebraic group over $\mathbb{C}$) and $V$ an irreducible finite-dimensional representation of $G$, determined by its highest weight. ...
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Do the values of the differential of a function on a Lie group with a single maximum span the Lie algebra?
Consider: a vector field $X=\nabla \phi$ on a compact, semi-simple, connected matrix Lie group $G$ where $\phi$ as a smooth scalar field on $G$ possessing only a single maxima which topologically is a ...
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Transitivity of $Spin(7)$ in triples of vectors
I have a simple question: transitivity of $Spin(7)$ in triples of orthogonal vectors. Let $Spin(7)\subset SO(8)$ act on $\mathbb{R}^8$, and $e_1,e_2,e_3$, $v_1,v_2,v_3$ be two triples of mutually ...
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Characterization of restricted weights of representations of real semisimple Lie groups
I need to use the following theorem:
Let $\mathfrak{g}$ be a semisimple real Lie algebra, $\Sigma$ a set of restricted roots for $\mathfrak{g}$. Let $\rho$ be any finite-dimensional representation of ...
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Todd class and Baker-Campbell-Hausdorff, or the curious number $12$
The number $12$ (or, probably we shall say Bernoulli numbers in general) appears in many places in Mathematics, sometimes leading to unexpected connections between different topics.
For instance, ...
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$Spin(7)$ as stabilizer of a $4$-form revisited
For a better understanding of this question, please see the question and answer here.
In $Spin(8)$ there are plenty of copies of $Spin(7)$; consider, for instance, the antiimage of $SO(7)<SO(8)$ ...
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How to prove a bracket is super anti-commutative?
On page 12 of the paper, there is a formula about super Poisson bracket on a Lie super group $G$:
\begin{align}
\{\phi, \psi\} = \sum_{\mu, \nu} (-1)^{|\phi||\nu|} r^{\mu \nu} ( R_{\mu} \phi R_{\nu} \...
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Is the exp map for the Lie group of positive functions on a manifold a global diffeo?
I asked this question on math stack exchange but figured I might get a quicker answer here. I included a bit more information at the end. Thank you for your help!
As I understand it, for the Lie ...
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Haar measure on $O(n)$ reduced to simpler probability space
The background of this question is how a random variable $X$ on the orthogonal group $O(n)$ whose distribution is the normalized Haar measure $\mu$, i.e., $\mu( O(n) ) = 1$, can be realized on a ...
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Orbits of an action of maximal compact subgroups of p-adic orthogonal groups
Let $Q$ be a non-degenerate indefinite quadratic form on ${\mathbb R}^n$ and write $G=SO(Q)$ for the associated special orthogonal group. Let $K$ be a maximal compact subgroup of $G$ and consider the ...
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Exceptional symmetric spaces with quaternionic structure
Following this and this question I found following chain of exceptional symmetric spaces being quaternionic manifolds. I listed dimensions as superscripts for reader convenience.
$F_{I}^{28}\subset ...
user21230
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Matrix from a homomorphism of simply connected groups
Let $H$ be a simple algebraic group of type $\mathbf{G}_2$ over $\mathbb{C}$.
Let $\rho$ be the standard 7-dimensional complex representation
$$ \rho\colon H=\mathbf{G}_2\to \mathrm{SO}_7.$$
We ...
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Postnikov Classes of Lie Groups
I'm interested in the low dimensional homotopy type of spaces like $SU(n)$. I know that the Whitehead products in cohomology vanish for all Lie groups. Does this mean that the Postnikov invariants (ie....
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An algorithm to compare two representations of a simple Lie algebra?
I have two representations of a simple (complex or real) finite-dimensional Lie algebra $S$, both given in terms of their structure constants on a given basis.
the first one is the adjoint ...
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Action of a Lie groupoid on a Lie Algebroid?
Let $\pi:E\longrightarrow M$ be a vector bundle. Then we can associate a Lie groupoid $\mathsf{Gl}(E)\rightrightarrows M$ where $$\mathsf{Gl}(E):=\{E_x\stackrel{lin. isom.}{\longrightarrow} E_y: x, y\...
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Regular functions on nilpotent orbits and their covers
Let $G$ be a complex semisimple algebraic group with Lie algebra $\mathfrak{g}$.
In 1989 McGovern described the structure (as $G$-module) of the ring of regular functions on a finite cover of the ...
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analytic structure on lie groups
I need a reference for a result I have heard only very vaguely "A lie group (smooth) has a compatible analytic manifold structure".
(Would even appreciate a concise way to refer to the result..)
I ...
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Iwasawa and $KAK$ Decomposition for Diff$(S^1)$
It is well known
$\newcommand{\Diff}{\operatorname{Diff}}$
that the group $\Diff(S^1)$ of smooth diffeomorphisms of the circle behaves in many ways like $SL(2,\mathbb R)$. For example, if $S^1\...
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Derivation of Blattner's conjecture in the Beilinson-Bernstein picture
On the last page of Schmid's article "Discrete Series", he says
"In the Beilinson-Bernstein picture, discrete series modules are attached to closed $K$-orbits in $X$... the $K_{\mathbb ...
- 27.9k
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1
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Tannaka–Krein duality
First I would like to stress that maybe I don't have a necessary background from the theory of Lie groups. I met the topic of Tannaka–Krein duality while reading the book of Gracia–Bondia, Varilly and ...
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SU(6) -> SU(3) branching rule
I read in at least one paper and in the wiki below
http://en.wikipedia.org/wiki/Quark_model
that the 56 symmetric irrep of SU(6) breaks down into 10^{3/2} + 8^{1/2}
irreps of SU(3)xSU(2). Here the ...
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Can Galois conjugates of lattices in SL(2,R) be discrete?
Let $\Gamma$ be a lattice in $SL(2,\mathbb{R})$. Suppose that the trace field of $\Gamma$ is a totally real number field of degree $d$. This gives $d$ homomorphisms $\rho_i:\Gamma\to SL(2,\mathbb{R})$ ...
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reference containing the list of irreducible finite dimensional representation of real general linear group
It seems that it is not easy to find a reference containing a classification and construction of finite dimensional irreducible representations of $GL_n(\mathbb{R})$. One way to look at it is via $(\...
- 2,709
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Number of orthogonal operators in representations of the Unitary Group
Let $G={\rm SU}(d)$ be the unitary group and $\rho(g)$ an irreducible representation of $g\in G$ in a $D$ dimensional Hilbert space $V$. Let $e_i\in V$ be the diagonal matrix whose only non-zero ...
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Local diffeomorphism from a torus to a Lie group
Let $G$ be a simple Lie group of dimension $n$ (connected or even simply connected). Let $T$ be a maximal torus of dimension $d$. Notice that $\frac{n}{d}$ is an integer which I will denote by $m$. ...
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Non-invariant Lagrangian on SU(n)
I have a Lagrangian on $SU(n)$, which is not invariant.
Given the Lagrangian $\mathcal{L}[U_t, \dot{U}_t] = \langle \dot{U}_t, \nabla J \big|_{U_t} \rangle$
I need to find the curves of stationary ...
- 2,099
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The space of Lie group homomorphisms
Let $\ \mathrm{Hom}(H,G)\ $ be the space of Lie group homomorphisms between compact connected Lie groups $H$, $G$. What is known about homology (or homotopy) groups of $\mathrm{Hom}(H,G)$?
UPDATE: $...
- 29.1k
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Symmetric pairs of holomorphic type
Let $G$ be a real simple Lie group of Hermitian type; that is, $G/K$ carries a structure of a Hermitian symmetric space where $K$ is a maximal compact subgroup of $G$. Equivalently, the center $Z(\...
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Bound on the index of an abelian subgroup in discrete subgroup of the euclidean group?
I asked the following question on math.SE a couple of days ago. Dietrich Burde gave an answer for the case that the subgroup is not only discrete but also acts cocompactly.
What about the general ...
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Is this sphere bundle over SL3/SO3 trivial?
The space $SL_3(\mathbb{R})/SO_3(\mathbb{R})$ can be though of as some kind of 5-(real)dimensional generalized upper half-space.
Fix any copy of $SO_2(\mathbb{R})$ sitting inside $SO_3(\mathbb{R})$, ...
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3
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Peter-Weyl theorem as proven in Cartier's Primer
I'm reading Pierre Cartier's A primer of Hopf algebras to educate myself. In its subsection 3.3 (which doesn't need any Hopf algebra theory), he sketches a proof why compact Lie groups are algebraic. ...
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Normal subgroup of the identity component of a linear Lie group is normal in the whole group?
Suppose $G$ is a linear Lie group (i.e. $G$ admits a finite dimensional faithful representation) and $G$ has finitely many connected components. Let $G_0$ be the identity component of $G$. If $N$ is a ...
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How to Evaluate the ABJM partition function for N=2
This is the ABJM partition function on the 3-sphere,
$$ Z(2) = \int \frac{d^2\mu}{(2\pi)^2} \frac{d^2\nu}{(2\pi)^2}
\frac{\left[ 2 \sinh \frac{\mu_1 - \mu_2}{2}\right]^2\left[ 2 \sinh \frac{\nu_1 - \...
- 22.8k
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Nilpotent Lie algebras and unipotent Lie groups
$\mathbf{n}$ is nilpotent Lie algebra with $N$ being the corresponding algebraic Lie group. Now one neat feature of this setting is that you can take the exponential map to be identity. In other words ...
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