December 8 (Thu) at 16:00 - 17:30, 2022 (JST)
  • Hybrid Format (Common Room 246-248 and Zoom)
Yuki Yokokura

The membrane paradigm provides a fascinating bridge between gravitational dynamics near black hole horizons (null boundaries) and fluid dynamics. One question naturally follows: what type of fluids and hydrodynamics emerged at the horizon? Contrary to the longstanding belief, it turns out that the horizon fluid is Carrollian, rather than the Galilean (Navier-Stokes) fluid. The Carroll geometries and Carrollian physics, arising originally when the speed of light goes to zero (c to 0 limit), have recently gained increasing attention in the fields of black hole physics and flat holography.
In this presentation, I will talk about the Carrollian limit and the resulting Carroll geometries and this unusual kind of hydrodynamics, the Carrollian hydrodynamics. I will then present the geometrical construction of the membrane (also known as the stretched horizon) in a way that a Carroll geometry manifest, therefore allowing us to spell out precisely the dictionary between gravitational degrees of freedom on the membrane and the Carrollian fluid quantities. I will also show that the Einstein’s equations projected onto the horizon are the Carrollian hydrodynamic conservation laws. Lastly, I will discuss the covariant phase space of the horizon, symmetries, and conservation laws. The talk is based on arXiv:2209.03328 and arXiv:2211.06415.


  1. Laurent Freidel, Puttarak Jai-akson, Carrollian hydrodynamics from symmetries, arXiv: 2209.03328
  2. Laurent Freidel, Puttarak Jai-akson, Carrollian hydrodynamics and symplectic structure on stretched horizons, arXiv: 2211.06415

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