nLab
almost connected topological group

Context

Group Theory

Topology

Contents

Definition

Definition

A locally compact topological group G is called almost connected if the underlying topological space of the quotient topological group G/G 0 (of G by the connected component of the neutral element, also called the identity component) is compact.

See for instance (Hofmann-Morris, def. 4.24). We remark that since the identity component G 0 is closed, the identity in G/G 0 is a closed point. It follows that G/G 0 is T 1 and therefore, because it is a uniform space, T 312 (a Tychonoff space; see uniform space for details). In particular, G/G 0 is compact Hausdorff.

Example

Every compact and every connected topological group is almost connected.

Also every quotient of an almost connected group is almost connected.

References

Textbooks with relevant material include

  • M. Stroppel, Locally compact groups, European Math. Soc., (2006)
  • Karl Hofmann Sidney Morris, The Lie theory of connected pro-Lie groups, Tracts in Mathematics 2, European Mathematical Society, (2000)

Original articles include

  • Chabert, Echterhoff, Nest, The Connes-Kasparov conjecture for almost connected groups and for linear p-adic groups (pdf)

Revised on February 3, 2012 22:02:40 by Todd Trimble (74.88.146.52)