Extend coupled radiative separation beyond Kerr–Newman–de Sitter

Extend exact separation of the coupled gravitational and electromagnetic radiative system to more general backgrounds, including relevant members of the Plebański–Demiański family and the Ovcharenko–Podolský solutions with a nonaligned electromagnetic field.

Background

The paper demonstrates exact separation for subextremal Kerr–Newman–de Sitter backgrounds and notes that local separation identities also apply on patches of Kerr–Newman–anti-de Sitter spacetime where the transformation is nonsingular.

It then identifies broader classes of algebraically structured backgrounds with hidden symmetries and related separated equations in approximations. Extending the exact coupled gravitational–electromagnetic separation to these settings is explicitly identified as unresolved.