## Abstract

We give a construction of a universal average of Lie algebra elements whose exponentiation gives (when there is an associated Lie group) a totally symmetric geometric mean of Lie group elements (sufficiently close to the identity) with the property that in an action of the group on a space X for which n elements all take a particular point a 2 X to a common point b 2 X, also the mean will take a to b. The construction holds without the necessity for the existence of a Lie group and the universal average μn(x1, . . . , xn) is a totally symmetric universal expression in the free Lie algebra generated by x1, . . . , xn . Its expansion up to three brackets is found explicitly and various properties of iterated averages are given. Although this is a purely algebraic result, it is expected to have applications in diverse fields. One known application is to the construction of explicit differential graded Lie algebra models of three dimensional cells and thereby to discretised differential geometry on cubulated manifolds. This work is based on the second author's minor thesis.

Original language | English |
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Pages (from-to) | 351-366 |

Number of pages | 16 |

Journal | Journal of Lie Theory |

Volume | 31 |

Issue number | 2 |

State | Published - 2021 |

### Bibliographical note

Publisher Copyright:© 2021 Heldermann Verlag.

## Keywords

- Baker-Campbell-Hausdorff formula
- DGLA
- Karcher mean
- Maurer-Cartan