Towards a naturally small cosmological constant from branes in 6D supergravity

Abstract

We investigate the possibility of self-tuning of the effective 4D cosmological constant in 6D supergravity, to see whether it could naturally be of order 1/r 4 when compactified on two dimensions having Kaluza-Klein masses of order 1/r. In the models we examine supersymmetry is broken by the presence of nonsupersymmetric 3-branes (on one of which we live). If r were sub-millimeter in size, such a cosmological constant could describe the recently-discovered dark energy. A successful self-tuning mechanism would therefore predict a connection between the observed size of the cosmological constant, and potentially observable effects in submillimeter tests of gravity and at the Large Hadron Collider. We do find self tuning inasmuch as 3-branes can quite generically remain classically flat regardless of the size of their tensions, due to an automatic cancellation with the curvature and dilaton of the transverse two dimensions. We argue that in some circumstances six-dimensional supersymmetry might help suppress quantum corrections to this cancellation down to the bulk supersymmetry-breaking scale, which is of order 1/r. We finally examine an explicit realization of the mechanism, in which 3-branes are inserted into an anomaly-free version of Salam-Sezgin gauged 6D supergravity compactified on a 2sphere with nonzero magnetic flux. This realization is only partially successful due to a topological constraint which relates bulk couplings to the brane tension, although we give arguments why these relations may be stable against quantum corrections.

The general warped solution with conical branes in six-dimensional supergravity

“…This choice corresponds to un-warped solutions that were considered in ref. [9] and (with multiple branes) in ref. [16].…”

“…For compact dimensions, the gauge flux is quantized in the presence of charged particles [5,9,10,13] as…”

Galileon Higgs vortices

“…It might be that such systems are related to -and find applications JHEP02 (2016)063 for -the SLED proposal pushed forward by Burgess and collaborators (see e.g. [32][33][34]), that makes use of the properties of codimension two object for addressing the cosmological constant problem. We leave these questions to further study.…”

String loop moduli stabilisation and cosmology in IIB flux compactifications

“…This is an interesting configuration because of the following observation: since t 2 = √ τ 1 and t 1 = (τ 2 − 2τ 1 )/2 √ τ 1 , we can see that τ 2 ≫ τ 1 would imply that t 1 ≫ t 2 and we would effectively have a very anisotropic compactification with the 2-cycle much bigger than its dual 4-cycle. This could then lead to a realisation of the supersymmetric 2 large extra dimensions scenario [19,187], in which the extra dimension could be as large as a fraction of a millimetre. This would correspond to looking for solutions Ω = (1 + ǫ) V with ǫ → 0.…”