Non-commutative Barge-Ghys quasimorphisms: an erratum

Abstract

This is an erratum to the paper ``Non-commutative Barge-Ghys quasimorphisms''. The effective version of Ambrose-Singer theorem used in this paper was mis-stated, making Theorem 3.11 false as stated. However, this statement remains true for a semidirect product $G=A⋊K$ of a non-compact Lie group with a compact Lie group $K$, as long as the curvature of the connection belongs to the Lie algebra of $K$. Theorems 3.12 and 3.22 remain true under this assumptions, the statements of Theorems 4.28 and 4.31 are modified accordingly. Theorem 5.2 is valid only for compact Lie groups.

The amended paper is available at http://verbit.ru/TeX/New-quasimorphisms.pdf or https://www.math.bgu.ac.il/~brandens/New-quasimorphisms.pdf