Stable non-BPS D-branes in Type I string theory

TL;DR

This paper uses boundary state formalism to analyze non-BPS D-branes in Type I string theory, demonstrating stability conditions, computing tensions, and aligning with K-theory classifications.

Contribution

It introduces a method to incorporate tachyon condensation effects into boundary states, explicitly constructs stable non-BPS D-branes, and matches K-theory predictions.

Findings

Identifies stable non-BPS D-branes in Type I string theory.

Calculates the mass and tension of these D-branes.

Confirms classification aligns with K-theory results.

Abstract

We use the boundary state formalism to study, from the closed string point of view, superpositions of branes and anti-branes which are relevant in some non-perturbative string dualities. Treating the tachyon instability of these systems as proposed by A. Sen, we show how to incorporate the effects of the tachyon condensation directly in the boundary state. In this way we manage to show explicitly that the D1 -- anti-D1 pair of Type I is a stable non-BPS D-particle, and compute its mass. We also generalize this construction to describe other non-BPS D-branes of Type I. By requiring the absence of tachyons in the open string spectrum, we find which configurations are stable and compute their tensions. Our classification is in complete agreement with the results recently obtained using the K-theory of space-time.