Local and global rigidity for isometric actions of simple Lie groups on pseudo-Riemannian manifolds

TL;DR

This paper establishes local and global rigidity results for isometric actions of simple Lie groups on pseudo-Riemannian manifolds, showing under certain conditions that such manifolds are locally or globally modeled on Lie groups with bi-invariant metrics.

Contribution

It proves new local and global rigidity theorems for isometric simple Lie group actions on pseudo-Riemannian manifolds, extending previous results to non-complete cases and low-dimensional settings.

Findings

Local rigidity holds for low-dimensional manifolds with non-integrable normal bundle.

Complete manifolds are, up to finite cover, quotients of Lie groups by lattices.

Rigidity results apply to actions of SO(p,q), G2(2), and F4 groups.

Abstract

Let $M$ be a finite volume analytic pseudo-Riemannian manifold that admits an isometric $G$-action with a dense orbit, where $G$ is a connected non-compact simple Lie group. For low-dimensional $M$, i.e. $\dim(M) < 2\dim(G)$, when the normal bundle to the $G$-orbits is non-integrable and for suitable conditions, we prove that $M$ has a $G$-invariant metric which is locally isometric to a Lie group with a bi-invariant metric (local rigidity theorem). The latter does not require $M$ to be complete as in previous works. We also prove a general result showing that $M$ is, up to a finite covering, of the form $H/\Gamma$ ($\Gamma$ a lattice in the group $H$) when we assume that $M$ is complete (global rigidity theorem). For both the local and the global rigidity theorems we provide cases that imply the rigidity of $G$-actions for $G$ given by $\mathrm{SO}_0(p,q)$, $G_{2(2)}$ or a non-compact simple Lie group of type $F_4$ over $\mathbb{R}$. We also survey the techniques and results related to this work.