D-branes and boundary states in closed string theories

In this Ph.D. thesis, we study some aspects of strings and branes. We mainly focus on anomalous D-brane couplings and on non-supersymmetric branes. In Chapter 2, we illustrate three key concepts in a field theory context: duality, supersymmetry and anomaly inflow. Chapter 3 contains an introduction to string theory, emphasizing the concepts relevant to this thesis, like string scattering amplitudes and D-brane actions. In Chapter 4, we introduce the boundary state formalism and use it to check the presence of anomalous couplings in the D-brane Wess-Zumino action. In addition, we show that this action also contains non-anomalous terms. Chapter 5 gives a BPS analysis of D-branes in D-brane backgrounds, focusing on the baryon vertex in the AdS/CFT correspondence. Chapter 6 is devoted to branes in type 0 string theory. We derive the D-brane Wess-Zumino action and the massless spectra of NS-fivebranes, and combine these ingredients to comment on type 0B S-duality. In Chapter 7, we study non-BPS D-branes in type II string theory. We propose a Wess-Zumino action for these branes, check it by computing string scattering amplitudes and show that it is consistent with the interpretation of BPS D-branes as topologically non-trivial tachyon configurations on a non-BPS D-brane.