We present an orbifold compactification of the minimal seven-dimensional supergravity. The vacuum is a slice of seven-dimensional anti–de Sitter space where six-branes of opposite tension are located at the orbifold fixed points. The cancellation of gauge and gravitational anomalies restricts the gauge group and matter content on the boundaries. In addition, anomaly cancellation fixes the boundary gauge couplings in terms of the gravitational constant, and the mass parameter of the Chern-Simons term.
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We thank C. Angelantonj, E. Kiritsis, J. March-Russell, E. Poppitz, R. Rattazzi, A. Sagnotti, J. Sonnen?>schein, and R. Sundrum for discussions. The work of T. G. was supported in part by a DOE Grant No. DE-FG02-94ER40823 at the University of Minnesota. The work of A. K. was supported in part by the European RTN networks HPRN-CT-2000-00122 and HPRN-CT-2000-00131. T. G. wishes to acknowledge the Aspen Center for Physics where part of this work was done.