Pseudo-Riemannian Symmetries on Heisenberg group ${\mathbb{H}}_3$

Abstract

The notion of $\Gamma$-symmetric space is a natural generalization of the classical notion of symmetric space based on $\z_2$-grading of Lie algebras. In our case, we consider homogeneous spaces $G/H$ such that the Lie algebra $\g$ of $G$ admits a $\Gamma$-grading where $\Gamma$ is a finite abelian group. In this work we study Riemannian metrics and Lorentzian metrics on the Heisenberg group ${\mathbb{H}}_3$ adapted to the symmetries of a $\Gamma$-symmetric structure on ${\mathbb{H}}_3$. We prove that the classification of $\z_2^2$-symmetric Riemannian and Lorentzian metrics on ${\mathbb{H}}_3$ corresponds to the classification of left invariant Riemannian and Lorentzian metrics, up to isometries. This gives examples of non-symmetric Lorentzian homogeneous spaces.

18 pages