Double-vector multiplet and partially broken N=4, d=3 supersymmetry
We elaborate on a new N=2, d=3 supermultiplet (double-vector multiplet) with a non-trivial off-shell realization of the central charge. Its bosonic sector comprises two abelian gauge vector fields forming an SO(2) vector. We present a superfield formulation of this multiplet in the central-charge extended N=2, d=3 superspace and then employ it, in the framework of the nonlinear realizations approach, as the Goldstone one for the partial breaking N=4 -> N=2 in three dimensions. The covariant equations of motion for the self-interacting Goldstone superfield arise as a natural generalization of the free ones and are interpreted as the worldvolume supersymmetric form of the equations of motion of a N=4 D2-brane. For the vector fields we find a coupled nonlinear system of Born-Infeld type and demonstrate its dual equivalence to the d=5 membrane. The double-vector multiplet can be fused with some extra N=2, d=3 multiplet to form an off-shell N=4, d=3 supermultiplet.