Worldsheet Instantons and a Null String Limit of Born-Infeld Theory

TL;DR

This paper introduces a modified Born-Infeld action for superstring theory in four dimensions, enabling a tensionless limit interpreted as null strings on D3-branes, potentially induced by worldsheet instantons.

Contribution

It proposes a new modification of the Born-Infeld action that admits a well-defined tensionless limit, linking null strings and nonperturbative worldsheet instanton effects.

Findings

Modified Born-Infeld action with tensionless limit

Interpretation of null strings on D3-branes

Connection to worldsheet instanton contributions

Abstract

For a superstring theory in four spacetime dimensions, we propose a modification of the Born-Infeld action that possesses a well-defined tensionless limit. We interpret this as describing the effective target space dynamics of null strings on a D3-brane. We argue that such a modification can be induced by nonperturbative contributions from instantons in the worldsheet sigma-model describing string propagation on the brane.