Cosmic D- and DF-strings from D3D̄3: Black Strings and BPS Limit

We study Dand DF-strings in a D3D̄3 system in the context of Dirac-Born-Infeld type effective field theory. In the presence of an electric flux from a transverse direction, we discuss gravitating thick D-string solutions of a spatial manifold, S2 × R1, in which straight D-strings stretched along the R1 direction are attached to the south and north poles of the two-sphere. There is a horizon along its equator which means the structure of black strings is formed. We also discuss the BPS limits for thin parallel Dand DF-strings in both flat and curved spacetime. The BPS sum rule is obtained for arbitrarily-separated multi-string configuration with a Gaussian type tachyon potential. At the site of each thin BPS D(F)string, the pressure takes a finite value. We find that there exists maximum deficit angle π in the conical geometry induced by thin BPS Dand DF-strings.