U-duality Invariant Quantum Entropy from Sums of Kloosterman Sums

TL;DR

This paper establishes a connection between the arithmetic properties of Kloosterman sums and the quantum entropy of supersymmetric black holes in AdS2, incorporating all quantum corrections and ensuring U-duality invariance.

Contribution

It introduces generalized Kloosterman sums with new arithmetic properties that reproduce non-primitive black hole degeneracies from bulk quantum gravity.

Findings

Recovered non-primitive degeneracies from bulk quantum gravity.

Matched the dependence on the torsion invariant in the  case.

Resolved a U-duality invariance puzzle for  BPS degeneracies.

Abstract

U-duality plays a special role in the study of the microscopic degrees of freedom of supersymmetric black holes. To be consistent with duality, the black hole quantum degeneracy must obey special arithmetic properties, which are non-perturbative in nature. In this work, we study these properties from a holographic point of view, establishing a connection between arithmetic properties of Kloosterman sums and quantum gravity in $\text{AdS}_2$ space. To this end, we consider the entropy of black holes that carry non-primitive charges, in both $\mathcal{N}=8$ and $\mathcal{N}=4$ four dimensional compactifications; our analysis includes all the perturbative and non-perturbative bulk quantum corrections. The key result relies on special arithmetic properties of generalized Kloosterman sums that we develop. These are a generalization of the known Selberg identity of classical Kloosterman sums. In both the $\mathcal{N}=8$ and $\mathcal{N}=4$ examples, we recover, from the bulk quantum gravity, the non-primitive answer which is a sum over the primitive degeneracies, depending non-trivially on the discrete duality invariants. In particular, for the $\mathcal{N}=4$ case we show that the quantum gravity answer reproduces the dependence on the torsion invariant $I=\text{gcd}(Q\wedge P)$, in agreement with the microscopic formulas. For the $\mathcal{N}=8$ case, we solve a puzzle related to U-duality invariance of the supergravity answer and the corresponding one-eighth BPS degeneracy.