  We study the cosmological evolution of a single BPS D-brane in the absence of
potential, which is in the category of the Chaplygin gas cosmological model.
When such a D-brane coupled to gravity moves in the bulk with a non-vanishing
velocity, it tends to slow down to zero velocity via mechanisms like
gravitational waves leakage to the bulk, losing its kinetic energy to fuel the
expansion of the universe on the D-brane. If the initial velocity of the
D-brane is high enough, the universe on the D-brane undergoes a dust-like stage
at early times and an acceleration stage at late times, as observed in the
original Chaplygin gas model. When the D-brane velocity is initially zero, the
D-brane will always remain fixed at some position in the bulk, with the brane
tension over the Plank mass squared as a cosmological constant. Interestingly,
this kind of fixed brane universe can arise as defects from tachyon inflation
on a non-BPS D-brane with one dimension higherWe study the cosmological
evolution of a single BPS D-brane coupled to gravity in the absence of
potential. When such a D-brane moves in the bulk with non-vanishing velocity,
it tends to slow down to zero velocity via mechanisms like gravitational wave
leakage to the bulk, losing its kinetic energy to fuel the expansion of the
universe on the D-brane. If the initial velocity of the D-brane is high enough,
the universe on the D-brane undergoes a dust-like stage at early times and an
acceleration stage at late times, realising the original Chaplygin gas model.
When the D-brane velocity is initially zero, the D-brane will always remain
fixed at some position in the bulk, with the brane tension over the Plank mass
squared as a cosmological constant. It is further shown that this kind of fixed
brane universe can arise as defects from tachyon inflation on a non-BPS D-brane
with one dimension higher.
