D-Brane Dynamics Near NS5-Branes

TL;DR

This paper investigates the real-time dynamics of a D-brane near NS5-branes using the Dirac-Born-Infeld action, revealing a pressureless fluid behavior and proposing decay into modes within the fivebrane throat, with exact solutions in certain regimes.

Contribution

It introduces a detailed analysis of D-brane decay near NS5-branes, linking tachyon condensation to radial modes and providing an exactly solvable conformal field theory description.

Findings

D-brane approaches pressureless fluid state near NS5-branes.

D-brane decays into modes in the fivebrane throat.

Exact worldsheet CFT describes radial motion deep inside the throat.

Abstract

We use the Dirac-Born-Infeld action to study the real time dynamics of a $Dp$-brane propagating in the vicinity of $NS5$-branes. This problem is closely related to tachyon condensation on an unstable D-brane, with the role of the tachyon played by the radial mode on the D-brane. As the D-brane approaches the fivebranes, its equation of state approaches that of a pressureless fluid. The pressure goes to zero at late times like $\exp(-\alpha t)$; $\alpha$ is a function of the number of fivebranes and of the angular momentum of the D-brane. For unstable D-branes a similar equation of state is taken to signal the decay of the D-brane into closed string radiation. We propose that in our case the D-brane decays into modes propagating in the fivebrane throat, and show that this is consistent with spacetime expectations. We also argue that for radial motions of the D-brane deep inside the throat, the rolling process is described by an exactly solvable worldsheet conformal field theory.