## Abstract

We prove that for any classical, compact, simple, connected Lie group G, the G-invariant orbital measures supported on non-trivial conjugacy classes satisfy a surprising L^{2}-singular dichotomy: Either μ_{h}^{k} ∈ L^{2} (G) or μ_{h}^{k} is singular to the Haar measure on G. The minimum exponent k for which μ_{h}^{k} ∈ L^{2} is specified; it depends on Lie properties of the element h ∈ G. As a corollary, we complete the solution to a classical problem - to determine the minimum exponent k such that μ^{k} ∈ L^{1} (G) for all central, continuous measures μ on G. Our approach to the singularity problem is geometric and involves studying the size of tangent spaces to the products of the conjugacy classes.

Original language | English |
---|---|

Pages (from-to) | 1521-1573 |

Number of pages | 53 |

Journal | Advances in Mathematics |

Volume | 222 |

Issue number | 5 |

DOIs | |

Publication status | Published - Dec 1 2009 |

Externally published | Yes |

## Keywords

- Compact Lie group
- Conjugacy class
- Orbital measure
- Singular measure
- Tangent space

## ASJC Scopus subject areas

- Mathematics(all)