Supersymmetry, p-brane duality and hidden space and time dimensions

A global superalgebra with 32 supercharges and all possible central extensions is studied in order to extract some general properties of duality and hidden dimensions in a theory that treats $p$-branes democratically. The maximal number of dimensions is 12, with signature (10,2), containing one space and one time dimensions that are hidden from the point of view of perturbative 10-dimensional string theory or its compactifications. When the theory is compactified on $R^{d-1,1}\otimes T^{c+1,1}$ with $d+c+2=12,$ there are isometry groups that relate to the hidden dimensions as well as to duality. Their combined classification schemes provide some properties of non-perturbative states and their couplings.