Comments on D-brane Dynamics Near NS5-Branes

TL;DR

This paper analyzes the dynamics of D-branes near NS5-branes, showing their behavior resembles non-BPS D-branes and exploring decay processes and energy emission characteristics.

Contribution

It demonstrates that D-brane behavior near NS5-branes mimics non-BPS D-branes and calculates decay cross-sections, providing insights into brane decay and string theory dynamics.

Findings

D-brane equation of state approaches pressureless fluid near NS5-branes

Decay cross-section diverges for D0, D1, D2 branes

Energy emission converges for higher-dimensional D-branes

Abstract

We study the properties of a D-brane in the presence of $k$ NS5 branes. The Dirac-Born-Infeld action describing the dynamics of this D-brane is very similar to that of a non-BPS D-brane in ten dimensions. As the D-brane approaches the fivebranes, its equation of state approaches that of a pressureless fluid. In non-BPS D-brane case this is considered as an evidence for the decay of the D-brane into ``tachyon matter''. We show that in our case similar behavior is the consequence of the motion of the D-brane. In particular in the rest frame of the moving D-brane the equation of state is that of a usual D-brane, for which the pressure is equal to the energy density. We also compute the total cross-section for the decay of the D-brane into closed string modes and show that the emitted energy has a power like divergence for $D0$, $D1$ and $D2$ branes, while converges for higher dimensional D-branes. We also speculate on the possibility that the infalling D-brane describes a decaying defect in six dimensional Little String Theory.