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Abstract: (arXiv)
The problem of gravitational fluctuations confined inside a finite cutoff at radius r=rcr=r_c outside the horizon in a general class of black hole geometries is considered. Consistent boundary conditions at both the cutoff surface and the horizon are found and the resulting modes analyzed. For general cutoff rcr_c the dispersion relation is shown at long wavelengths to be that of a linearized Navier-Stokes fluid living on the cutoff surface. A cutoff-dependent line-integral formula for the diffusion constant D(rc)D(r_c) is derived. The dependence on rcr_c is interpreted as renormalization group (RG) flow in the fluid. Taking the cutoff to infinity in an asymptotically AdS context, the formula for D()D(\infty) reproduces as a special case well-known results derived using AdS/CFT. Taking the cutoff to the horizon, the effective speed of sound goes to infinity, the fluid becomes incompressible and the Navier-Stokes dispersion relation becomes exact. The resulting universal formula for the diffusion constant D(horizon)D(horizon) reproduces old results from the membrane paradigm. Hence the old membrane paradigm results and new AdS/CFT results are related by RG flow. RG flow-invariance of the viscosity to entropy ratio η/s\eta /s is shown to follow from the first law of thermodynamics together with isentropy of radial evolution in classical gravity. The ratio is expected to run when quantum gravitational corrections are included.
  • Classical Theories of Gravity
  • Black Holes
  • Holography and condensed matter physics (AdS/CMT)
  • field theory: conformal
  • renormalization group: flow
  • quantum gravity: correction
  • gravitation: fluctuation
  • gravitation: classical
  • velocity: acoustic
  • horizon