In September 2009, TRF readers could have learned about the work by
The extremal Kerr black hole in the conventional 3+1 dimensions has no supersymmetry but Guica et al. could calculate its entropy from the states in a two-dimensional CFT, anyway. However, you may still say that the black holes had to be "extremal" which plays the same role as "supersymmetric" even though these are not supersymmetric. However, in a new paper by Alejandra Fidel Castro, Alexander Maloney, and Andy Strominger (CMS, not to be confused with ATLAS),
Only in the extremal limit J=M^2, you can derive the conformal symmetry geometrically. But if you assume that the symmetry exists for all M,J, you can see that the the periodicity of the azimuthal "phi" angle makes the Euclidean time periodic so that the left-moving and right-moving temperatures are
TL = M2 / 2 pi J,The central charges are
TR = sqrt(M4 - J2) / 2 pi J.
cL = cR = 12 Jwhich immediately allows you to compute the entropy via Cardy's formula:
Smicro = (pi2 / 3) (cL TL + cR TR) = ...The story seems to be so self-consistent that you may want to trust it even though they don't actually "derive" the existence of the dual CFT. In fact, even if the CFT doesn't actually "exist", it seems that the calculation based on the assumption that it does leads to the right result.
... = Area/4.
Of course, I have had no doubts that the microscopic entropy - calculated by sufficiently authentic stringy methods - works correctly for all black holes since the 1990s. But it's still fun to see that some of these calculations may actually be simpler than we may have previously expected.