Cosmological evolution of a D-brane

TL;DR

This paper investigates the cosmological evolution of a BPS D-brane, showing how its velocity affects universe expansion stages and how fixed branes can emerge from tachyon inflation, linking string theory to cosmology.

Contribution

It introduces a model of D-brane cosmology where brane velocity influences universe dynamics, connecting tachyon inflation to fixed brane universes.

Findings

High initial D-brane velocity leads to early dust-like and late acceleration stages.

D-brane velocity tends to decrease to zero due to gravitational wave leakage.

Fixed brane universes can originate from tachyon inflation on non-BPS D-branes.

Abstract

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.