D-branes with Lorentzian signature in the Nappi-Witten model

TL;DR

This paper constructs Lorentzian signature D-branes of various dimensions in the Nappi-Witten string model by solving a differential problem for non-automorphism isometries, including degenerate cases.

Contribution

It introduces a method to construct D-branes with Lorentzian signature in the Nappi-Witten model using a differential approach for non-automorphism isometries.

Findings

Constructed Lorentzian D-branes of all dimensions in the Nappi-Witten model.

Solved the gluing condition as a well-posed differential problem.

Obtained metrically degenerate D-branes.

Abstract

Lorentzian signature D-branes of all dimensions for the Nappi-Witten string are constructed. This is done by rewriting the gluing condition $J_+=FJ_-$ for the model chiral currents on the brane as a well posed first order differential problem and by solving it for Lie algebra isometries $F$ other than Lie algebra automorphisms. By construction, these D-branes are not twined conjugacy classes. Metrically degenerate D-branes are also obtained.