BPS and near-BPS black holes in $AdS_5$ and their spectrum in $\mathcal{N}=4$ SYM
We study quantum corrections in the gravitational path integral around nearly $1/16$-BPS black holes in asymptotically $AdS_5 \times S^5$ space, dual to heavy states in 4D $\mathcal{N}=4$ super Yang-Mills. The analysis provides a gravitational explanation of why $1/16$-BPS black holes exhibit an exact degeneracy at large $N$ and why all such states have the same charges, confirming the belief that the superconformal index precisely counts the entropy of extremal black holes. We show the presence of a gap of order $N^{-2}$ between the $1/16$-BPS black holes and the lightest near-BPS black holes within the same charge sector. This is the first example of such a gap for black holes states within the context of $AdS_5$ holography. We also derive the spectrum of near-BPS states that lie above this gap. Our computation relies on finding the correct version of the $\mathcal{N}=2$ super-Schwarzian theory which captures the breaking of the $SU(1, 1|1)$ symmetry when the black hole has finite temperature and non-zero chemical potential. Finally, we comment on possible stringy and non-perturbative corrections that can affect the black hole spectrum.