Folding Branes

TL;DR

This paper analyzes the nonlinear dynamics of a probe Dp-brane in a Dp-brane background, revealing how inhomogeneous ripples grow and lead to brane folding, with implications for string cosmology.

Contribution

It provides a full analytical treatment of inhomogeneous brane dynamics with arbitrary runaway potentials, extending understanding of brane behavior in BPS backgrounds.

Findings

Inhomogeneous ripples grow over time, causing brane folding.

Near-horizon dynamics can be described by free streaming relativistic particles.

Limitations arise at self-crossing loci (caustics) in the effective action.

Abstract

We study classical dynamics of a probe Dp-brane moving in a background sourced by a stack of Dp-branes. In this context the physics is similar to that of the effective action for open-string tachyon condensation, but with a power-law runaway potential. We show that small inhomogeneous ripples of the probe brane embedding grow with time, leading to folding of the brane as it moves. We give a full nonlinear analytical treatment of inhomogeneous brane dynamics, suitable for the Dirac-Born-Infeld + Wess-Zumino theory with arbitrary runaway potential, in the case where the source branes are BPS. In the near-horizon geometry, the inhomogeneous brane motion has a dual description in terms of free streaming of massive relativistic test particles originating from the initial hypersurface of the probe brane. We discuss limitations of the effective action description around loci of self-crossing of the probe brane (caustics). We also discuss the effect of brane folding in application to the theory of cosmological fluctuations in string theory inflation.