Cycling in the Throat

TL;DR

The paper investigates brane cosmology within warped string backgrounds by treating a D3-brane (or anti-D3-brane) as a moving probe governed by the Dirac-Born-Infeld action and its Wess-Zumino coupling. It develops a general framework for probe-brane dynamics in warped throats (AdS5, KT, KS) and analyzes how internal angular momentum, via conserved quantities, introduces a centrifugal barrier that slows radial motion and generates turning points. The main contributions are (i) showing that angular momentum can induce brane bounces and, in certain parameter ranges within KT/KS throats, bound orbits corresponding to cyclic universes, and (ii) providing explicit expressions for the radial velocity and induced cosmology, including the FRW form on the brane with $a(\tau)=h^{-1/4}$ and the brane-observer Hubble parameter. These results reveal new stringy phenomenology for early-universe cosmology and highlight the potential of angular motion in internal dimensions to alter inflaton dynamics and yield cyclic cosmologies without requiring brane collisions.

Abstract

We analyse the dynamics of a probe D3-(anti-)brane propagating in a warped string compactification, making use of the Dirac-Born-Infeld action approximation. We also examine the time dependent expansion of such moving branes from the ``mirage cosmology'' perspective, where cosmology is induced by the brane motion in the background spacetime. A range of physically interesting backgrounds are considered: AdS5, Klebanov-Tseytlin and Klebanov-Strassler. Our focus is on exploring what new phenomenology is obtained from giving the brane angular momentum in the extra dimensions. We find that in general, angular momentum creates a centrifugal barrier, causing bouncing cosmologies. More unexpected, and more interesting, is the existence of bound orbits, corresponding to cyclic universes.