  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.
