External Fields and the Dynamics of Fundamental Flavours in Holographic Duals of Large N Gauge Theories

Abstract: Using the gauge-gravity duality we study strongly coupled dynamics of fundamental flavours in large N_c gauge theories in a constant external field. We primarily focus on the effects of an external magnetic field. We use two holographic models realized in the Type IIB and Type IIA supergravity and present a comparative case study. In both these models, by studying the dynamics of probe branes, we explicitly demonstrate and discuss the magnetically induced chiral symmetry breaking effect ("magnetic catalysis") in the flavour sector. We also study the associated thermodynamics and the meson spectrum and realize e.g. Zeeman splitting, stability enhancement of the mesons in the presence of an external magnetic field etc. By studying the quasinormal modes of the probe brane fluctuation in the hydrodynamic limit we also obtain an analytic dispersion relation in the presence of a magnetic field in the Type IIA model. This dispersion relation consists of a propagating sound mode in the otherwise diffusive channel and is sourced by the quantum anomaly of the global U(1) current. We briefly discuss the effects of an external electric field and observe that the flavour bound states dissociate for sufficiently high electric fields and an electric current is induced.