Cutoffs, Stretched Horizons and Black Hole Radiators
  We argue that if the UV cutoff of an effective field theory with many low
energy degrees if freedom 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 rate may not be enhanced by the
emission of all the light IR modes. Instead, there may be additional
suppressions hidden in the UV completion of the field theory, which really
control which light modes can be emitted by the black hole. It could turn out
that many degrees of freedom cannot be efficiently emitted by the black hole,
and so the radiance rate may be much smaller than its estimate based on the
counting of the light IR degrees of freedom. 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 4D s-waves of bulk modes with small 5D momentum, or equivalently,
small 4D masses. Further, their emission is suppressed by bulk warping, which
lowers the radiation rate much below the IR estimate, yielding a radiation flux
$\sim (T_{BH} L)^2 {\cal L}_{hawking} \sim (T_{BH}/M_{Pl})^2 N {\cal
L}_{hawking}$, where ${\cal L}_{hawking}$ is the Hawking radiation rate of a
single light species. This 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, $M_{Pl}^2 \simeq N \mu^2$.
