A Picture of D-branes at Strong Coupling

TL;DR

The authors reformulate the Born-Infeld action for D-branes in phase space and analyze the strong coupling (tensionless) limit $T\to 0$, which corresponds to $g\to\infty$ via $T_p=\frac{2\pi}{g(2\pi\sqrt{\alpha'})^{p+1}}$ with $g=e^{\phi}$. They derive a first-order action and show how $T\to0$ yields a degenerate world-volume metric, leading to a parton picture in which the D-brane behaves as a collection of tensile strings (for $p>1$) or a unified description of tensile and tensionless strings (for $p=1$). In this tensionless regime, the dynamics factorizes into two-dimensional internal directions, described by a degenerate zweibein and a 2D Lorentzian tangent space, with the string sheets governed by light-cone-like equations $\gamma_{++}=\gamma_{--}=0$ and $\partial_+\partial_-X^\mu=0$. The work points to intriguing connections with matrix models and higher-dimensional theories, and suggests avenues for supersymmetric extensions of the tensionless D-brane framework.

Abstract

We use a phase space description to (re)derive a first order form of the Born-Infeld action for D-branes. This derivation also makes it possible to consider the limit where the tension of the D-brane goes to zero. We find that in this limit, which can be considered to be the strong coupling limit of the fundamental string theory, the world-volume of the D-brane generically splits into a collection of tensile strings.