SOLITONIC BRANE WORLD WITH COMPLETELY LOCALIZED (SUPER)GRAVITY

Abstract

We construct a solitonic three-brane solution in the five-dimensional Einstein–Hilbert–Gauss–Bonnet theory. This solitonic brane is δ-function-like, and has the property that gravity is completely localized on the brane. That is, there are no propagating degrees of freedom in the bulk, while on the brane we have purely four-dimensional Einstein gravity. Thus, albeit the classical background is five-dimensional, the quantum theory (perturbatively) is four-dimensional. Our solution can be embedded in the supergravity context, where we have completely localized supergravity on the corresponding solitonic brane, which is a BPS object preserving 1/2 of the original supersymmetries. By including a scalar field, we also construct a smooth domain wall solution, which in a certain limit reduces to the δ-function-like solitonic brane solution (this is possible for the latter breaks diffeomorphisms only spontaneously). We then show that in the smooth domain wall background the only normalizable mode is the four-dimensional graviton zero mode, while all the other (including massive Kaluza–Klein) modes are not even plane-wave normalizable. Finally, we observe that in compactifications of Type IIB on five-dimensional Einstein manifolds other than a five-sphere the corresponding dual gauge theories on D3-branes are not conformal in the ultraviolet, and at the quantum level we expect the Einstein–Hilbert term to be generated in their world volumes. We conjecture that in full string theory on Type IIB side this is due to higher curvature terms, which cannot be ignored in such backgrounds. A stronger version of this conjecture also states that (at least in some cases) in such backgrounds D3-branes are solitonic objects with completely localized (super)gravity in their world volumes.