The bound state of D1-branes and D5-branes in IIB string theory is an exceptionally fertile system for the study of black holes. The D1D5 system has two, dual descriptions: a gravitational and a conformal field theory (CFT) description. Here, we focus on using the two-dimensional CFT to understand black hole physics.
After reviewing the D1D5 system, we first show how to perturbatively relax the decoupling limit to calculate the emission out of the AdS/CFT into the asymptotic flat space. We take the effect of the neck into account and fix the coupling between the CFT and the asymptotic flat space. This calculation is distinguished from other AdS-CFT calculations which only work in the strict decoupling limit and use the gravitational description to learn about strongly coupled field theory.
We apply the formalism to particular smooth, horizonless three-charge nonextremal geometries. In the fuzzball proposal, these geometries are interpreted as black hole microstates, but they suffer from a classical instability. At first, the instability seems problematic in the fuzzball proposal; however, it was argued that if one used the D1D5 CFT then the instability could be interpreted as precisely the Hawking radiation process for the particular microstates. That the instability is classical, and not quantum mechanical results from a large Bose enhancement. In this document, we perform calculations that confirm this interpretation and demonstrate the above emission formalism.
All of the calculations discussed thus far, and most of the calculations in the literature on the D1D5 CFT, are at the "orbifold point" in moduli space. This point is far from the black hole physics of interest, but some calculations agree anyway. To understand black holes better it seems likely that moving off of the orbifold point will become necessary. We present several calculations demonstrating the effect of a single application of the marginal deformation operator that moves the D1D5 CFT off its orbifold point. The deformation operator twists two copies of the orbifold CFT, which we show produces a "squeezed state" with an arbitrary number of excitations. Thus, initial high-energy excitations can fragment into many low-energy excitations. This deformation, should give rise to thermalization and other important black hole dynamics.
Finally, we close with a brief summary and mention some opportunities for future work.