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Cosmas Zachos, "Extended Supergravity with a Gauged Central Charge", Caltech Ph.D. Thesis, (1979), [1]; "N=2 Supergravity Theory With A Gauged Central Charge", Phys. Lett. B, 76, (1979), pp. 329–332. doi:10.1016/0370-2693(78)90799-2
David Pollard, "Antigravity and classical solutions of five-dimensional Kaluza-Klein theory", J. Phys. A, 16, (1983), pp. 565–574, doi:10.1088/0305-4470/16/3/015.