examples of non-matrix Lie groups

While most well-known Lie groups are matrix groups, there do in fact exist Lie groups which are not matrix groups. That is, they have no faithful finite dimensional representations.

For example, let $H$ be the real Heisenberg group

H=\left\{\begin{pmatrix}1&a&b\\ 0&1&c\\ 0&0&1\end{pmatrix}\mid a,b,c\in\mathbb{R}\right\},

and $\Gamma$ the discrete subgroup

\Gamma=\left\{\begin{pmatrix}1&0&n\\ 0&1&0\\ 0&0&1\end{pmatrix}\mid n\in\mathbb{Z}\right\}.

The subgroup $\Gamma$ is central, and thus normal. The Lie group $H/\Gamma$ has no faithful finite dimensional representations over $\mathbb{R}$ or $\mathbb{C}$ .

Another example is the universal cover of $\mathrm{SL}_{2}\mathbb{R}$ . $\mathrm{SL}_{2}\mathbb{R}$ is homotopy equivalent to a circle, and thus $\pi(\mathrm{SL}_{2}\mathbb{R})\cong\mathbb{Z}$ , and thus has an infinite-sheeted cover. Any real or complex representation of this group factors through the projection map to $\mathrm{SL}_{2}\mathbb{R}$ .

Title	examples of non-matrix Lie groups
Canonical name	ExamplesOfNonmatrixLieGroups
Date of creation	2013-03-22 13:20:48
Last modified on	2013-03-22 13:20:48
Owner	bwebste (988)
Last modified by	bwebste (988)
Numerical id	6
Author	bwebste (988)
Entry type	Example
Classification	msc 17B10
Related topic	AdosTheorem