Open/Closed Duality, Unstable D-Branes, and Coarse-Grained Closed Strings

TL;DR

This paper demonstrates a precise classical correspondence between the fluid description of unstable D-brane decay and macroscopic stretched closed strings, revealing insights into string-fluid duality and tachyon matter as high-frequency string energy.

Contribution

It establishes a detailed classical equivalence between the decay fluid system and macroscopic closed strings, elucidating the role of tachyon matter and string undulations.

Findings

Exact match of fluid and string motion at classical level.

String fluid captures low frequency undulations.

Tachyon matter encodes high frequency oscillations.

Abstract

At the final stage of unstable D-brane decay in the effective field theory approach, all energy and momentum of the initial state are taken up by two types of fluids, known as string fluid and tachyon matter. In this note, we compare motion of this fluid system to that of macroscopic collection of stretched closed strings and find a precise match at classical level. The string fluid reflects low frequency undulation of the stretched strings while the tachyon matter encodes the average effect of high frequency oscillations turned on those strings. In particular, the combined fluid system has been known to have a reduced speed of light, depending on the composition, and we show that this property is exactly reproduced in classical motion on the closed string side. Finally we illustrate how the tachyon matter may be viewed as an effective degrees of freedom carrying high frequency energy-momentum of Nambu-Goto strings by coarse-graining the dynamics of the latter.