Tachyon condensation in unbalanced D-anti D system
  The tachyon condensation is studied in asymmetric D-anti D systems. Taking a system of two pairs of D5-anti D5 in type IIB superstring theory in the background of large N D5-branes, we show that one BPS D1-brane comes out after the condensation. It is also seen that the BPS D1-brane feels no force from the background D5-branes. We also show that the inclusion of the fluctuation fields gives an expected Dirac-Born-Infeld (DBI) action of the resultant D1-brane. On the other hand, in the case of one pair of D5-anti D5 in the same background, we show that the resultant BPS D3-brane experiences attractive force from the background D5-branes. 
Akira Ishida, Shozo Uehara, Tomoki Yada