Using the D1D5 CFT to Understand Black Holes

TL;DR

The dissertation uses the D1D5 system as a concrete arena to explore quantum gravity and black hole microphysics via AdS3/CFT2 holography and the fuzzball proposal. It develops a formalism to couple the D1D5 CFT to asymptotically flat space, enabling microscopic calculations of emission spectra that reproduce Hawking‑like radiation from specific microstate geometries. By analyzing the orbifold CFT and its marginal deformations, spectral flow, and twist operators, the work reveals how high‑energy D1D5 states can fragment into many low‑energy excitations and how ergoregion emission in JMaRT geometries matches CFT predictions. The results provide nontrivial tests of the fuzzball idea and offer a controlled, calculable bridge between gravity and microscopic CFT descriptions of black holes. Overall, the work strengthens the view that black hole thermodynamics can be understood through a unitary holographic microscopic framework in string theory, with explicit maps between bulk geometries and boundary states.

Abstract

In this dissertation, we review work presented in arXiv:0906.2015, arXiv:0907.1663, arXiv:1002.3132, arXiv:1003.2746, and arXiv:1007.2202 on the D1D5 system. We begin with some motivational material for black holes in string theory. In Chapter 2, we review the D1D5 system, including the gravity and CFT descriptions. In Chapter 3, we show how to perturbatively relax the decoupling limit in a general AdS-CFT setting. This allows one to compute the emission out of the AdS/CFT into the asymptotic flat space. In Chapter 4, we apply that formalism to some particular geometries, and exactly reproduce the emission spectrum. These geometries are interpreted as fuzzball microstates of a black hole, and the emission as the microscopic analogue of the Hawking radiation. In Chapter 5, we discuss how to deform the D1D5 CFT off of its orbifold point. In particular, we present full off-shell expressions for first-order corrections to the CFT states. One can see how high-energy states can fragment into many lower-energy states. In the conclusion, we discuss some opportunities for future work.

Figures (28)

• Figure 1: The Penrose diagram for some matter (light blue) collapsing into a Schwarzschild black hole. Outside of the matter, the metric is Schwarzschild. The Penrose diagram does not correctly indicate distances between spacetime events; only angles are correctly indicated. Null geodesics are lines at $\pm 45^\circ$, like the green dashed curve illustrating the connection between coordinates on future null infinity, $\mathcal{J}^+$, and past null infinity, $\mathcal{J}^-$. The gray shading on $\mathcal{J}^+$ and $\mathcal{J}^-$ indicates the region where geometric optics is a good approximation.
• Figure 2: A closed string splits into two closed strings in the "pants diagram." Note that a single worldsheet describes this three-point function. Thus the string worldsheet description is far richer than the analogous worldline theory of a particle.
• Figure 3: A closed string propagating through time sweeps out a worldsheet. We parameterize the worldsheet with functions $X(\sigma,\tau)$. We can think of $X$ as fields living in a two-dimensional field theory with coordinates $(\sigma, \tau)$.
• Figure 4: A cartoon illustrating the sum over all possible topologies of the interacting string.
• Figure 5: An illustration of the different ways that open strings can be configured on D-branes. The long arrows indicate the polarization of the open string, not its velocity, which has been suppressed.