Twin supergravities

We study the phenomenon that pairs of supergravities can have identical bosonic field content but different fermionic extensions. Such twin theories are classified and shown to originate as truncations of a common theory with more supersymmetry. Moreover, we discuss the possible gaugings and scalar potentials of twin theories. This allows us to pinpoint to which extent these structures are determined by the purely bosonic structure of the underlying Kac-Moody algebras and where supersymmetry comes to play its role. As an example, we analyse the gaugings of the six-dimensional N = (0, 1) and N = (2, 1) theories with an identical bosonic sector and explicitly work out their scalar potentials. The discrepancy between the potentials finds a natural explanation within maximal supergravity, in which both theories may be embedded.