I review some marginal deformations of SU(2) and SL(2, R) Wess–Zumino–Witten models , which are relevant for the investigation of the moduli space of NS5/F1 brane configurations. Particular emphasis is given to the asymmetric deformations, triggered by electric or magnetic fluxes. These exhibit critical values, where the target spaces become exact geometric cosets such as S 2 ≡ SU(2)/U(1) or Ad...