D-branes in a Big Bang/Big Crunch Universe: Nappi-Witten Gauged WZW Model

Abstract

We study D-branes in the Nappi-Witten model, which is a gauged WZW model based on (SL(2,R) x SU(2)) / (U(1) x U(1)). The model describes a four dimensional space-time consisting of cosmological regions with big bang/big crunch singularities and static regions with closed time-like curves. The aim of this paper is to investigate by D-brane probes whether there are pathologies associated with the cosmological singularities and the closed time-like curves. We first classify D-branes in a group theoretical way, and then examine DBI actions for effective theories on the D-branes. In particular, we show that D-brane metric from the DBI action does not include singularities, and wave functions on the D-branes are well behaved even in the presence of closed time-like curves.

50 pages, 2 figures, minor changes

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• D-Brane solutions in a light-like linear dilaton background
• Black Hole - String Transition and Rolling D-brane
• Anti-de Sitter D-brane dynamics
• D1-brane with Overcritical Electric Field in AdS3 and S-brane
• Fractional S-branes on a Spacetime Orbifold
• Geometric construction of D-branes in WZW models