## BPS D-branes from an unstable D-brane in a curved background

We find exact tachyon kink solutions of Dirac-Born-Infeld-type effective action describing an unstable D5-brane with a world volume 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 R{sup 1,4}xT{sup 2}xS{sup 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 R{sup 1,2}xT{sup 2} where T{sup 2} is inside S{sup 3}. In one class of solutions we find an infinite degeneracy with respect to a constant magnetic fieldmore »