On the quantum width of a black hole horizon

Dec, 2003

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Abstract:
The many low energy modes near a black hole horizon give the thermal atmosphere a divergent entropy which becomes of order A/4GA/4G with a Planck scale cut-off. However, Sorkin has given a Newtonian argument for 3+1 Schwarzschild black holes to the effect that fluctuations of such modes provide the horizon with a non-zero quantum mechanical width. This width then effectively enforces a cut-off at much larger distances so that the entropy of the thermal atmosphere is negligible in comparison with A/4GA/4G for large black holes. We generalize and improve this result by giving a relativistic argument valid for any spherical black hole in any dimension. The result is again a cut-off LcL_c at a geometric mean of the Planck scale and the black hole radius: in particular, LcdRTHpd2L_c^d \sim \frac{R}{T_H} \ell_p^{d-2}. With this cut-off, the entropy of the thermal atmosphere is again parametrically small in comparison with the Bekenstein-Hawking entropy of the black hole. The effect of a large number NN of fundamental fields and the discrepancies from naive predictions of a stretched horizon model are also discussed.
  • talk: Dubrovnik 2003/09/04
  • black hole: horizon
  • entropy
  • horizon: width
  • black hole: Schwarzschild
  • horizon: fluctuation