Cutoffs, Stretched Horizons and Black Hole Radiators

Who: Nemanja Kaloper (UC Davis, California)
When: Thursday, May 24, 2012 at 14:15
Where: FKF’s colloquia room

We argue that if the UV cutoff of the IR theory is of the order, or below, the scale of the stretched horizon in a black hole background, which in turn is significantly lower than the Planck scale, the black hole radiance is controlled by the UV completion of the field theory. In particular, if the UV completion of the theory involves degrees of freedom which cannot be efficiently emitted by the black hole, the naive radiance rate estimated by the counting of the IR degrees of freedom may be dramatically reduced. If we apply this argument to the RS2 brane world, it implies that the emission rates of the low energy CFT modes will be dramatically suppressed: its UV completion is given by the bulk gravity on $AdS_5 \times S^5$, and the only bulk modes that could be emitted by a black hole are the s-waves of bulk modes with small 4D masses. But their emission is suppressed by bulk warping. This lowers the radiation rate much below the IR estimate, and follows directly from low CFT cutoff $\mu \sim L^{-1} \ll M_{Pl}$, a large number of modes $N \gg 1$ and the fact that 4D gravity in RS2 is induced, $M_{Pl}^2 \simeq N \mu^2$.