2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/185141We construct solutions in purely gravitational bulk with flat vacuum branes without fine tuning the constants of the theory. Our solutions incorporate one or two branes and have topology S^1 x R^4 without Z_2 symmetry. They are not invariant under the four-dimensional Lorentz group effectively acting on the brane, but the significance of this fact will become clear only after the study of their perturbations.9 pages, revtex. Text enlarged; version to appear in PLBHigh Energy Physics - PhenomenologyGeneral Relativity and Quantum CosmologyHigh Energy Physics - Theorytext