Abstract :
We construct supergravity theories in twelve and thirteen dimensions with tes respective signatures (10, 2) and (11, 2) with some technical details. Starting with N = 1 supergravity in 10+2 dimensions coupled to Green-Schwarz superstring, we give N = 2 chiral supergravity in 10+2 dimensions with its couplings to super (2 + 2)-brane. We also build an N = 1 supergravity in 11+2 dimensions, coupled to supermembrane. All of these formulations utilize scalar (super) fields intact under supersymmetry, replacing the null-vectors introduced in their original formulations. This method makes all the equations SO(10, 2) or SO(11, 2) Lorentz covariant, up to modified Lorentz generators. We inspect the internal consistency of these formulations, in particular with the usage of the modified Lorentz generators for the extra coordinates.
