High Energy Theory Seminar

I describe why spacetime is not a great place to do physics if one is interested in the exact dynamics of spinning black holes, and why it must be recast into a more fundamental structure. Spinspacetime is a complex four-manifold that unifies spacetime and spin as its real and imaginary parts. Its special-relativistic concept was envisioned by Ezra Ted Newman in the 70s, but its complete mathematical formulation in general relativity has been only recently established. The Poisson brackets of spinspacetime exhibit a characteristic "zig-zag" pattern, tracing back to the Kähler geometry of massive twistor space. This complex geometry dictates the Newman-Janis property of spinning black holes in their point-particle effective theory, revealing hypothetical particle components of the Kerr black hole—"zig" and "zag"—that implements white and black blobs in "massive Hodges diagrams" in terms of a graviton helicity selection rule. These particles are not hypothetical at all: it is shown that the Kerr black hole represents a dipolar "bar magnet" of dyonic masses (Taub-NUT instantons), from which the Newman-Janis algorithm is deciphered in the faithful relativist fashion. Practical applications and explicit outcomes of spinspacetime will be showcased: systematic derivations of the Bargmann-Michel-Telegdi (BMT) or Mathisson-Papapetrou-Dixon (MPD) equations and their all-orders-in-spin extensions, conserved quantities and exact superintegrability in the self-dual sector, spin-resummed scattering amplitudes, and gravitational-wave physics.

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