Non-BPS D-Branes in Light-Cone Green-Schwarz Formalism

TL;DR

This paper develops a covariant description of non-BPS D-branes in type IIB string theory using light-cone Green-Schwarz formalism, analyzing boundary states and conformal field theories with consistency checks and novel boundary conditions.

Contribution

It introduces a covariant framework for non-BPS D-branes in Green-Schwarz formalism, including a new doubling trick for bi-local boundary conditions and consistency verification methods.

Findings

Open string spectrum matches boundary state predictions

Boundary conditions expressed with bi-local fermionic fields

Correlation functions computed without boundary insertions

Abstract

Non-BPS D-branes are difficult to describe covariantly in a manifestly supersymmetric formalism. For definiteness we concentrate on type IIB string theory in flat background in light-cone Green-Schwarz formalism. We study both the boundary state and the boundary conformal field theory descriptions of these D-branes with manifest SO(8) covariance and go through various consistency checks. We analyze Sen's original construction of non-BPS D-branes given in terms of an orbifold boundary conformal field theory. We also directly study the relevant world-sheet theory by deriving the open string boundary condition from the covariant boundary state. Both these methods give the same open string spectrum which is consistent with the boundary state, as required by the world-sheet duality. The boundary condition found in the second method is given in terms of bi-local fields that are quadratic in Green-Schwarz fermions. We design a special ``doubling trick'' suitable to handle such boundary conditions and prescribe rules for computing all possible correlation functions without boundary insertions. This prescription has been tested by computing disk one-point functions of several classes of closed string states and comparing the results with the boundary state computation.