  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.
