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Abstract

We show that the Newman-Janis shift property of the exact Kerr solution can
be interpreted in terms of a worldsheet effective action. This holds both in
gravity, and for the single-copy $\sqrt{\text{Kerr}}$ solution in
electrodynamics. At the level of equations of motion, we show that the
Newman-Janis shift holds also for the leading interactions of the Kerr black
hole. These leading interactions are conveniently described using chiral
classical equations of motion with the help of the spinor-helicity method
familiar from scattering amplitudes.