Origin of additional Kerr QNM multiplets in the Schwarzschild limit

Determine whether the additional quasinormal-mode multiplets observed near the Schwarzschild algebraically special frequency in Kerr black holes correspond, in the limit a→0, to Schwarzschild algebraically special modes or to unconventional (branch-cut sheet) modes.

Background

Additional QNM sequences (multiplets) have been reported near algebraically special frequencies in Kerr spectra. Their appearance has been linked, in part, to possible splitting of unconventional modes predicted to lie beyond the branch cut, but numerical evidence has been inconclusive.

Clarifying the Schwarzschild-limit origin of these Kerr multiplets (AS versus unconventional) is crucial to resolve the longstanding ambiguity about their physical status and to understand the correct Zeeman-like splitting structure of overtones.