Unstable Non-BPS D-Branes of Type-II String Theories in Light-Cone Green-Schwarz Formalism

TL;DR

This paper constructs boundary states for unstable non-BPS D-branes in type-II string theories using the light-cone Green-Schwarz formalism, connecting current algebra techniques with GS variables.

Contribution

It provides a new formulation of non-BPS D-brane boundary states in light-cone GS formalism via current algebra and Ishibashi states, addressing covariance issues.

Findings

Boundary states expressed in terms of Ishibashi states

Reexpression of boundary states in Green-Schwarz variables

Derived known boundary state expressions from current algebra

Abstract

The problem of describing the boundary states of unstable non-BPS D-branes of type-II string theories in light-cone Green-Schwarz (GS) formalism is addressed. Regarding the type II theories in light-cone gauge as different realizations of the $\hat{SO}(8)_{k=1}$ Kac-Moody algebra, the non-BPS D-brane boundary states of these theories are given in terms of the relevant Ishibashi states constructed in this current algebra. Using the expressions for the current modes in terms of the GS variables it is straightforward to reexress the boundary states in the GS formalism. The problem that remains is the lack of manifest SO(8) covariance in these expressions. We also derive the various known expressions for the BPS and non-BPS D-brane boundary states by starting with the current algebra Ishibashi states.