Non-threshold D-brane bound states and black holes with non-zero entropy

TL;DR

The paper constructs a broad set of non-threshold BPS bound states by applying SL(2,Z) electromagnetic duality and boosts to intersecting M-branes, revealing that brane angles correspond to world-volume gauge-field flux and that these bound states yield new embeddings of 4D/5D black holes with entropies that depend on the angle. By reducing and T-dualizing these solutions, the authors obtain angled D-brane configurations and general families $(p⊥(p+2)|(p+2)⊥p)$ across multiple p, with SUSY preserved under specific angle regimes. They compute explicit entropy formulas for the resulting black holes, showing how the microscopic D-brane picture, including flux condensates, accounts for the angle-dependent entropy and its quantization. The work links non-perturbative dualities, brane bound states at angles, and black-hole microstate counting, providing a framework for exploring world-volume gauge theories and their role in black hole thermodynamics.

Abstract

We start with BPS-saturated configurations of two (orthogonally) intersecting M-branes and use the electro-magnetic duality or dimensional reduction along a boost, in order to obtain new p-brane bound states. In the first case the resulting configurations are interpreted as BPS-saturated non-threshold bound states of intersecting p-branes, and in the second case as p-branes intersecting at angles and their duals. As a by-product we deduce the enhancement of supersymmetry as the angle approaches zero. We also comment on the D-brane theory describing these new bound states, and a connection between the angle and the world-volume gauge fields of the D-brane system. We use these configurations to find new embeddings of the four and five dimensional black holes with non-zero entropy, whose entropy now also depends on the angle and world-volume gauge fields. The corresponding D-brane configuration sheds light on the microscopic entropy of such black holes.