A critical cosmological constant from millimeter extra dimensions

Abstract

We consider 'brane universe' scenarios with standard-model fields localized on a 3-brane in 6 spacetime dimensions. We show that if the spacetime is rotationally symmetric about the brane, local quantities in the bulk are insensitive to the couplings on the brane. This potentially allows compactifications where the effective 4-dimensional cosmological constant is independent of the couplings on the 3-brane. We consider several possible singularity-free compactification mechanisms, and find that they do not maintain this property. We also find solutions with naked spacetime singularities, and we speculate that new short-distance physics can become important near the singularities and allow a compactification with the desired properties. The picture that emerges is that standard-model loop contributions to the effective 4-dimensional cosmological constant can be cut off at distances shorter than the compactification scale. At shorter distance scales, renormalization effects due to standard-model fields renormalize the 3-brane tension, which changes a deficit angle in the transverse space without affecting local quantities in the bulk. For a compactification scale of order 10 −2 mm, this gives a standard-model contribution to the cosmological constant in the range favored by cosmology. Revised

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

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Anisotropic modulus stabilisation: strings at LHC scales with micron-sized extra dimensions

“…Although it remains an unsolved problem as to how this dynamics works in string theory, the effects of on-brane loops [83][84][85][86] and back-reaction [26,27,[87][88][89][90] have been studied for non-supersymmetric, codimension-2 branes in simpler 6D extra-dimensional models. These simpler systems resemble their 10D cousins in that the back-reaction is also competitive with bulk physics in stabilising the extra dimensions, yet doesn't destroy the presence of large-volume solutions.…”

Bulk stabilization, the extra-dimensional Higgs portal and missing energy in Higgs events

“…is the spin-summed Standard Model Higgs amplitude squared, p j represent the neutron four-momenta, and everything else maintains its old definition, except that it is now appropriate to use Maxwell-Boltzman distributions for the non-relativistic neutrons with number density n N 61) and in the phase space measures E j → m N , where m N is the nucleon mass.…”

“…For illustrative purposes (following the discussion of [14]) we do so here ignoring the energetics of the gravitational back-reaction of the branes. This is known not to be a good approximation in general for codimension-2 objects since in many cases it is the classical bulk back-reaction that cancels the brane tensions to allow the classical brane geometries to be flat [24,30,61]. (Indeed, it is this property -together with bulk supersymmetry -that underlies their use as a starting point for seeking solutions to the cosmological constant problem [25,27,62].)…”