Global extensions and causal structure of the broader family

Determine how acceleration and NUT-like twist affect maximal extensions, accessible singularities, and the causal roles of Killing horizons in the broader generalized black-hole family beyond the explicitly matched Kerr–Newman–Bertotti–Robinson subclasses.

Background

The paper explains that recent studies have constructed extensions across coordinate surfaces such as $r=\infty$ for Kerr–Bertotti–Robinson and Kerr–Newman–Bertotti–Robinson geometries. The correspondence established in the paper allows those results to be transferred to certain non-accelerating, effective-NUT-free subclasses.

For the more general solutions containing acceleration and NUT-like twist, the maximal extensions and causal interpretation remain unresolved. In particular, it is not established which coordinate surfaces can be extended through, which singularities are accessible, or how the various Killing horizons function globally.