Global and asymptotic properties of self-gravitating nonlinear sigma models

Abstract

We present an analytical study of the global and asymptotic properties of static, spherically symmetric, asymptotically flat solutions in general relativity and its \(D\)-dimensional generalization with multiple minimally coupled scalar fields described by a general nonlinear sigma model. Assuming a complete Riemannian target space and a non-negative scalar potential satisfying suitable growth conditions, we prove that solutions remain regular at every finite nonzero radius and can be extended inward to a naked singularity at the center. In particular, this excludes singularities on spherical shells at finite radius. We further show that all solutions exhibit universal asymptotic behavior near the central singularity. Finally, we demonstrate that these spacetimes can possess at most one photon sphere, which, if present, is necessarily unstable.