Open and Closed Strings from Unstable D-branes

TL;DR

This paper investigates the nature of electric flux tube solutions in tachyon effective field theory of unstable D-branes, proposing new interpretations involving open and closed strings and analyzing their geometric and energetic properties.

Contribution

It demonstrates that electric flux tubes can only end on BPS branes if embedded in finite tachyon regions, and offers a novel interpretation of flux tubes and tachyon matter as string systems.

Findings

Electric flux tubes must be embedded in finite tachyon regions to end on BPS branes.

Transverse area of flux tubes must vanish due to energetic constraints.

Original flux tube solutions may represent closed strings at high density.

Abstract

The tachyon effective field theory describing the dynamics of a non-BPS D-$p$-brane has electric flux tube solutions where the electric field is at its critical value and the tachyon is at its vacuum. It has been suggested that these solutions have the interpretation of fundamental strings. We show that in order that an electric flux tube can `end' on a kink solution representing a BPS D-$(p-1)$-brane, the electric flux must be embedded in a tubular region inside which the tachyon is finite rather than at its vacuum where it is infinite. Energetic consideration then forces the transverse `area' of this tube to vanish. We suggest a possible interpretation of the original electric flux tube solutions around the tachyon vacuum as well as of tachyon matter as system of closed strings at density far above the Hagedorn density.