K-302
Rigidity for extremal horizons
open Rigidity / Uniqueness
Statement
Extend black-hole rigidity and axisymmetry results to extremal stationary horizons where nondegeneracy assumptions fail.
Mathematical prerequisites
Degenerate horizon geometry; near-horizon expansion; unique continuation in degenerate settings; Killing field extension.
Why it matters
Extremal horizons fall outside some of the standard rigidity machinery.
Completion criteria
A complete answer must prove the existence of the needed symmetry or identify a counterexample under natural hypotheses.
Implications if solved
Would clarify whether extremal stationary black holes are as rigid as their nonextremal counterparts.
Last updated: 2026-04-05 ·
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