BPS D-branes from an Unstable D-brane in a Curved Background

Abstract

We find exact tachyon kink solutions of DBI type effective action describing an unstable D5-brane with worldvolume gauge field turned on in a curved background. The background of interest is the ten-dimensional lift of the Salam-Sezgin vacuum and, in the asymptotic limit, it approaches ${\mathrm{R}}^{1,4}\times {\mathrm{T}}^2\times {\mathrm{S}}^3$. The solutions are identified as composites of lower-dimensional D-branes and fundamental strings, and, in the BPS limit, they become a D4D2F1 composite wrapped on ${\mathrm{R}}^{1,2}\times {\mathrm{T}}^2$ where ${\mathrm{T}}^2$ is inside ${\mathrm{S}}^3$. In one class of solutions we find an infinite degeneracy with respect to a constant magnetic field along the direction of NS-NS field on ${\mathrm{S}}^3$.

16 pages, 2 figures, a footnote added, typos corrected and a reference added