Hybrid brane worlds in the Salam-Sezgin model

We construct a 6-dimensional warped brane world compactification of theSalam-Sezgin supergravity model by generalizing an earlier hybrid Kaluza-Klein/ Randall-Sundrum construction [hep-th/0109099]. In this construction theobserved universe is interpreted as a 4-brane in six dimensions, with aKaluza-Klein spatial direction in addition to the usual three noncompactspatial dimensions. This construction is distinct from other brane worldconstructions in six dimensions, which introduce the universe as a 3-branecorresponding to a topological defect in six dimensions, or which require aparticular configuration of matter fields on the brane. We demonstrate that themodel reproduces localized gravity on the brane in the expected form of aNewtonian potential with Yukawa-type corrections. We show that allowedparameter ranges include values which potentially solve the hierarchy problem.An exact nonlinear gravitational wave solution on the background is exhibited.The class of solutions given applies to Ricci-flat geometries in fourdimensions, and consequently includes brane world realizations of theSchwarzschild and Kerr black holes as particular examples. Arguments are givenwhich suggest that the hybrid compactification of the Salam-Sezgin model can beextended to reductions to arbitrary Einstein space geometries in fourdimensions.Comment: 27 pages, 2 figures, JHEP3.cls; v3 small additional sub-section consistent with published versio